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Colorectal cancer (CRC) is the third most common malignancy worldwide. It is projected to increase by 3.2 million new cases and account for 1.6 million deaths by 2040. Mortality is largely due to limited treatment options for patients who present with advanced disease. Thus, the development of effective and tolerable therapies is crucial. Chemotherapy has been the backbone of systemic treatment of advanced CRC, but utility has been limited because of invariable resistance to therapy, narrow mechanisms of action, and unfavorable toxicity profile. Tumors that are mismatch repair-deficient have demonstrated remarkable response to immune checkpoint inhibitor therapy. However, most CRC tumors are mismatch repair-proficient and represent an unmet medical need. Although ERBB2 amplification occurs only in a few cases, it is associated with left-sided tumors and a higher incidence of brain metastasis. Numerous combinations of HER2 inhibitors have demonstrated efficacy, and antibody-drug conjugates against HER2 represent innovative strategies in this area. The KRAS protein has been classically considered undruggable. Fortunately, new agents targeting KRAS G12C mutation represent a paradigm shift in the management of affected patients and could lead the advancement in drug development for the more common KRAS mutations. Furthermore, aberrant DNA damage response is present in 15%-20% of CRCs, and emerging innovative combinations with poly (ADP-ribose) polymerase (PARP) inhibitors could improve the current therapeutic landscape. Multiple novel biomarker-driven approaches in the management of patients with advanced CRC tumors are reviewed in this article.

Recent studies have identified durable responses with the use of immune checkpoint inhibitors in patients with mismatch repair–deficient (MMR-D)/microsatellite instability–high (MSI-H) metastatic colorectal cancer (CRC). The dramatic improvement in clinical outcomes led to the US Food and Drug Administration approval of pembrolizumab, nivolumab, and nivolumab in combination with ipilimumab in metastatic patients with MSI-H/MMR-D CRC who previously experienced progression on cytotoxic therapies. In the clinical trials investigating these agents, HIV-seropositive patients were not included and therefore the clinical efficacy of these agents in patients with metastatic MSI-H/MMR-D CRC living with HIV is unclear. On the basis of growing evidence, immune checkpoint blockade therapies seem to be a safe approach in patients with well-controlled HIV infection. Research on immunotherapeutic approaches in patients living with HIV and cancer is an area of unmet medical need that can be addressed by clinical trial designs that are inclusive of patients with well-controlled seropositive HIV and trials that specifically evaluate immune therapies in patients living with HIV.

198 Background: HER2 overexpression/amplification (HER2+) occurs in 3%-5% of patients (pts) w/ metastatic colorectal cancer (mCRC). Rates of HER2+ can increase to ~10% in pts w/ RAS/BRAF wild-type mCRC tumors. The MOUNTAINEER trial (NCT03043313) evaluated the efficacy and safety of the investigational combination of tucatinib with trastuzumab in pts with HER2+ and RAS wild-type mCRC. Established regional guidelines for mCRC recommend HER2 testing and HER2-directed treatment options; however, there is currently no established best practice for HER2 testing and interpretation in mCRC. Here, we present data from a concordance analysis comparing breast and gastric HER2 testing algorithms in the mCRC setting. Methods: The MOUNTAINEER trial enrolled pts w/ HER2+ mCRC identified using ≥1 method: tissue-based local immunohistochemistry (IHC), in situ hybridization (ISH), and/or next-generation sequencing (NGS) testing. Archival or fresh tumor tissue was submitted to a sponsor-designated central laboratory for confirmatory HER2 testing w/ IHC/FISH per the package insert of the FDA approved assay and scored by both the breast and gastric algorithms for HER2 IHC. A positive result per the breast scoring criteria for IHC requires circumferential membrane staining for HER2, while the gastric criteria allows for circumferential, basolateral, or lateral staining patterns. Results: A total of 114 pts were enrolled with HER2+ tumors per ≥1 local testing methods; 69 pts were HER2+ by NGS, 46 by IHC 3+, and 36 by ISH. Of 105 pts who had tissue available for central HER2 testing w/IHC/FISH, 98 had valid HER2 results; 82/98 (83.7%) of pts had tumors centrally confirmed as HER2+ using both the breast and gastric algorithms. Tissue samples from pts in the MOUNTAINEER trial had 100% concordance between breast and gastric algorithms in HER2 status and 99% concordance in HER2 IHC score. Conclusions: Central pathology testing using both the breast and gastric criteria showed high concordance between these two commonly used algorithms. A high central confirmation rate of local HER2+ results was also observed. These data support the use of either the breast or gastric algorithms to identify HER2+ mCRC tumors until an FDA-approved HER2 assay is available for mCRC. Clinical trial information: NCT03043313 . [Table: see text]

225 Background: HR deficient (HRD) CRC has improved outcomes following exposure to DNA damaging agent (DDA) (irinotecan, IR; oxaliplatin, OX) compared to HRP CRC. Low expression of wild type (WT) BRCA1 mRNA is associated with prolonged OS in ovarian cancer; however, this finding has not been investigated in CRC or outside of BRCA. Here, we examine the effect of low expression of HR genes in HRP CRC on post-DDA survival. Methods: 12,860 CRC samples were analyzed by NGS (592, NextSeq; WES, NovaSeq) and WTS (NovaSeq) at Caris Life Sciences (Phoenix, AZ). Samples were classified by RNA expression percentiles. Real world OS was extracted from insurance claims and calculated using Kaplan-Meier estimates for molecularly defined cohorts from first of OX or IR to last contact. Results: Post-IR survival was prolonged with low expression of ATM, CHEK2 and PALB2 in WT ATM, PALB2, and CHEK2 WT CRC, respectively (bottom vs. top 10%, bottom vs. top 25%; p

92 Background: Since the publication of the MOSAIC trial, stage III CC has been treated with a six-month (mo) regimen of FOLFOX (fluorouracil, leucovorin, and oxaliplatin) or CAPOX (capecitabine and oxaliplatin). Recently, the IDEA collaboration challenged this practice by demonstrating that the 3-year rate of disease-free survival (DFS) was non-inferior to 6mo of treatment (Rx) when given for low risk CC (83.1 vs. 83.3%) and resulted in significantly lower rates of grade 2 and higher neuropathy. In high risk (T4, N2) patients (pts) the DFS of 3mo of CAPOX was equivocal to 6mo (64.1 vs. 64.0%), while 3mo of FOLFOX was inferior to 6mo (61.5 vs. 64.7%). We hypothesized that trends in prescribing would favor shorter courses of Rx with a preference towards CAPOX given its efficacy across both high and low risk CC. Methods: We performed a retrospective analysis of stage III CC pts from 4 institutions. We evaluated prescribing patterns of 3mo or 6mo of Rx and CAPOX vs. FOLFOX over a period of 5 years from Jan 2016 to Jan 2021, a time period that traverses before and after the release of IDEA. Logistic and multinomial logistic regression models, with a linear time trend, were used to estimate the percentage of pts receiving CAPOX vs. FOLFOX and the combination of Rx and duration, respectively, while adjusting for baseline characteristics. The prescribing patterns in important subgroups were examined by incorporating the interaction term in the models. Results: A total of 366 pts met inclusion criteria. From 2016-2021, there was a significant increase per quarter in patients treated with CAPOX when compared to FOLFOX (OR 1.16 95% CI 1.11 – 1.21, p

4 Background: About 10-20% of patients with anal squamous cell carcinoma (SCCa) present with metastatic disease, and are usually treated with systemic chemotherapy. The role of local therapy to control the primary tumor is controversial in this setting. We evaluated survival impact of local therapy in metastatic anal SCCa. Methods: Data were obtained from all US hospitals that contributed to the National Cancer Database (NCDB) between 2004 and 2015. We excluded patients who did not receive palliative systemic chemotherapy. Univariate (UVA) and multivariable analyses (MVA) were performed to identify factors associated with patient outcome. Kaplan-Meier analysis and Cox proportional hazards models were used to assess the association between tumor/patient characteristics and overall survival (OS). Results: 1,160 patients were identified over 12 years. Median age was 57 years. Majority were female (64.9%), non-Hispanic Whites (79.1%) and had Charlson-Deyo Score of 0 (83.6%). Most common metastatic sites were liver (25.9%), lung (11.6%) and bone (8.5%). More than 79% of the patients received radiation to the primary site, and 10.4% underwent surgical resection for local control. Use of local therapy correlated closely with a significant improvement in OS on MVA (HR 0.66; 0.55-0.79; p < 0.001), with a 12-month and 5-year OS rates of 72.8% and 25.7% respectively, compared with 61.1% and 14.6% for patients treated with chemotherapy only. Poor prognostic factors included male gender (HR 1.44; 1.24-1.67; p < 0.001), age > 70 years (HR 1.28; 1.02-1.62; p = 0.034), lack of health insurance (HR 1.32; 1.02-1.71; p = 0.034), and cloacogenic zone location (HR 4.02; 1.43-11.30; p = 0.008). There was no benefit from abdominoperineal resection (mOS = 19.7mos; HR 1.05; 0.48-2.29; p = 0.909), but both local resection of the primary (mOS = 24.8mos, HR 0.48; 0.29-0.80; p = 0.005) and palliative radiation (mOS = 22.6 mos; HR 0.66; 0.55-0.79; p < 0.001) were associated with improved OS. Conclusions: This is the largest reported study on management of de novo stage IV SCCa. The data suggest that local control of the primary tumor through resection or radiation improved OS in patients with anal SCCa. Patients unlikely to benefit from local therapy include age over 70 years, male, lack of health insurance and cloacogenic carcinoma.

194 Background: Patients (pts) with multiple synchronous colon cancer primaries (MCPs) constitute a unique subset of pts with colon cancer. However, there are limited published studies about these pts. The objective of this study is to compare the characteristics and outcomes of pts with MCPs to those with single colon cancer primaries (SCPs) using the largest study population to date. Methods: Data was obtained from the Surveillance, Epidemiology, and End Results (SEER) database between 2004 and 2015. Pts with synchronous MCPs were included and were matched 1:3 with pts with SCPs based on the Coarsened Exact Matching method for age, gender, and race. Only patients with multiple synchronous primaries were included (time since index = 0 months). We excluded pts with a lag time since diagnosis of index primary of 1 month or more. Univariate (UNA) and multivariable (MVA) analyses were performed to identify factors associated with patient outcomes. Kaplan-Meier analyses and Cox proportional hazards models were used to assess the association between tumor/patient characteristics and overall survival (OS). Results: A total of 3322 pts with MCPs and 9966 pts with SCPs were identified. Median age was 71 years. Majority were male (51.5%) and White (80.1%). 73.4% and 69.6% of pts had 12 or more lymph nodes examined for the MCPs and SCPs cohorts, respectively. The SCPs cohort included more T4 stage and more well- and moderately-differentiated histology. OS was significantly shorter in MCPs compared to SCPs (HR 1.29; 1.22-1.36; p < 0.001), with a 5- and 10-year OS rate of 47.8% and 28.2% for the MCPs and 56.4% and 41.6% for the SCPs, respectively, for all stages combined. In the MCPs cohort, the use of adjuvant chemotherapy was associated with an improved survival in AJCC stages II, III, and IV but not stage I. Conclusions: This is the largest study evaluating the impact of MCPs on outcomes. Across stages II to IV, pts with MCPs have a shorter survival than those with SCPs. Pts with stage II MCPs who receive adjuvant chemotherapy derive a survival benefit. Current guidelines do not list multiple synchronous primaries as a high-risk feature for stage II.

TPS626 Background: Interleukin-6 (IL-6) is associated with carcinogenesis, immune suppression, and poor prognosis in pancreatic adenocarcinoma (PDAC). Preclinical data demonstrated dual inhibition of IL-6 and (programmed death ligand-1) PD-L1 facilitates CD8+ T cell migration into pancreatic tumors and was effective in controlling tumor growth in syngeneic and genetically engineered PDAC mouse models. Siltuximab is a chimeric monoclonal antibody which targets the IL-6 molecule specifically and spartalizumab is a high-affinity ligand-blocking humanized IgG4 antibody against the PD-1 receptor. Based on this preclinical rationale, we developed a phase Ib/II trial to determine the recommended phase II dose (RP2D), evaluate the safety, toxicity profile, preliminary antitumor activity, and immunogenicity of the siltuximab and spartalizumab in patients with previously treated metastatic PDAC. Methods: The phase Ib trial design is standard 3+3. Primary endpoint is to determine RP2D. Siltuximab is administered intravenously (IV) in three dose levels of 6 mg/kg (DL1), 11 mg/kg (DL2), 9 mg/kg (only if 2 DLTs observed on DL2) every 3 weeks with spartalizumab at 300 mg IV every 3 weeks. Eligible patients must have stage IV PDAC who have failed at least one prior therapy age ≥18 years, ECOG PS 0-1, no prior anti PD-1 or anti-PD-L1 agent. After RP2D is established, an expansion phase will enroll 24 patients with PDAC. Pre and on-treatment biopsy will be performed in 24 patients in the expansion cohort for correlative analysis. Pre-treatment and on-treatment peripheral blood samples will be collected from all patients. In the expansion phase patients will receive initial cycle (every 3 weeks) treatment with either spartalizumab or spartalizumab plus siltuximab and then starting cycle 2 all patients receive the combination following the on-treatment research biopsy. This design will enable us to evaluate the immunological effects of spartalizumab alone versus the combination in the tumor microenvironment and peripheral blood. This study was activated in January 2020 and to date 12 patients were enrolled in dose escalation phase. The dose expansion phase has recently started accrual. Clinical trial information: NCT04191421.

563 Background: RUB is an oral PARP1,2,3 inhibitor that demonstrated efficacy in patients (pts) with ovarian and prostate cancers harboring deleterious BRCA mutations. RUB exerts synergistic anti-tumor effect with IRI preclinically though the combination has overlapping toxicities. We previously published on the population PK of nal-IRI (Adiwijaya, Ma et al, Clin Pharm Ther 2017). We conducted a phase I study to evaluate a novel sequential dosing of RUB with nal-IRI/5FU in mGI cancer pts. Methods: Eligible pts had incurable mGI cancer previously received > 1 line of therapy (rx), ECOG PS 0-1, had RECIST measurable disease, adequate organ reserves and not received IRI for metastatic disease. Previous PARPi rx was excluded. The endpoints included dose limiting toxicity (DLT), maximum tolerated dose (MTD) and toxicity profile. The dose escalation utilized the 3+3 design. RUB was given oral bid on Day 4 to 13 and 18 to 27 with nal-IRI i.v. and 5FU i.v. 2400 mg/m2 over 46 hr on Day 1 and 15, every 28 day. Planned dose levels were RUB 400 mg/nal-IRI 50 mg/m2 (DL1), 400 mg/70 mg/m2 (DL2) and 600 mg/70 mg/m2 (DL3). Adverse events (AEs) were scored per CTCAE v4.03. Molecular profile was evaluated by CLIA-certified NGS testing. Results: Eighteen pts including 11 colorectal (CRC), 6 PANC, 1 gastroesophageal (GE) were enrolled and 12 were evaluable for DLTs. DL2 was not tolerable (DLT: G3 diarrhea, nausea and vomiting) and DL2A was added (RUB 600 mg/nal-IRI 50 mg/m2). DL2A enrolled 6 pts with no DLT and was determined as the MTD. Of DLT-evaluable pts, G3 and worse treatment-related AEs from all cycles were diarrhea (33%), fatigue (25%), leukopenia (25%), neutropenia (25%), anemia (8%) and nausea (8%). Four of 12 response evaluable pts had partial response: 2 CRC (1 had ATM mut), 1 PANC ( ATM mut), 1 GE ( BRCA2 mut) whilst 3 responders previously had platinum (PLA). Five pts had stable disease beyond 16 weeks (range 18.9 to 100.7 weeks), and all had prior PLA. Conclusions: The study successfully determined the MTD of RUB in combination with nal-IRI and 5FU. Encouraging efficacy was observed in PLA-treated mGI cancers including responses in those harboring ATM and BRCA alterations. The study is proceeding to evaluate the efficacy of the combination in metastatic pancreas cancer pts with and without BRCA1/2 or PALB2 alterations. Clinical trial information: NCT03337087.

e16259 Background: Colloid carcinoma (CC) of the pancreas is a rare histopathological subtype of ductal adenocarcinoma (PDAC), with poorly defined prognostic factors and therapeutic outcomes. The aim of this study is to characterize the clinicopathological features and evaluate the overall survival (OS) and prognostic factors of patients with pancreatic CC using National Cancer Database (NCDB). Methods: Patients diagnosed with CC of the pancreas and PDAC between 2004 and 2016 were identified from the NCDB using ICD-O-3 morphology (8480/3 for CC and 8140/3 for PDAC) and topography codes (C25). Univariate and multivariable analyses were conducted and Kaplan-Meier analysis and Cox proportional hazards models were used to perform OS analysis. Results: A total of 56,846 patients met the inclusion criteria for the final analysis. Of the total population included, 2,430 patients (4.3%) had CC and 54,416 patients (95.7%) had PDAC. For both, CC and PDAC, there was a male preponderance (52.0%, 52.5%), Caucasians (85.1%, 84%), occurrence above the age of 70 (39.2%, 38.2%), and the most common primary site was the head of the pancreas (50.5%, 53%). For CC, the percentage of pathologic stage III colloid pancreas cancer appeared the lowest (3.5%, 85 patients), compared to stage I (16.7%), stage II (37.8%), and stage IV (42.1%). While in PDAC, the percentage of pathologic stage I (5.94%) and stage III (4.44%) patients was lower than stage II (37.21%) and IV (52.41%). CC and PDAC more frequently presented with < 5cm tumor, at academic or research cancer centers, and diagnosed between 2009 and 2013 compared to 2004–2008 ( p< 0.001). For both CC and PDAC, the majority underwent surgical resection (58%, 53%), systemic chemotherapy (57.8%, 63%) and did not receive radiotherapy (78.8%, 77.6%). A positive surgical margin on pathologic evaluation was associated with worse outcomes for CC and PDAC in both univariate and multivariate analysis (HR 1.61; 1.56–1.66; p< 0.001 and HR 1.43; 1.38–1.48, p< 0.001). CC had a better 1-year overall survival (OS) in all stages compared to PDAC (p < 0.001). In multivariate analysis, mucinous carcinoma histology, female sex, diagnosis between 2004 and 2009, well/moderately differentiated histology, chemotherapy, age at diagnosis less than 60, radiation therapy after surgery, and local surgical procedure of primary site and pancreatectomy (p < 0.001) were associated with better OS compared to PDAC. Colloid histology was associated with better 1-year overall survival (OS) in all stages compared to PDAC (p < 0.001). Conclusions: Colloid carcinoma of pancreas is associated with a better overall survival as compared to pancreatic ductal adenocarcinoma. This is the largest study to address the clinical features and outcomes of colloid carcinoma of pancreas.

e16085 Background: Treatment of localized esophageal, gastroesophageal junction (GEJ), and stomach cancer is neoadjuvant therapy with either chemoradiation or chemotherapy followed by surgery. Treatment for T1b-2 stage disease is not well evaluated and this stage is underrepresented in prospective studies. The aim of this study is to evaluate survival outcomes among the three treatment modalities (neoadjuvant chemotherapy (NACT), neoadjuvant chemoradiation (NACRT), and upfront surgery (US)) in this population using the National Cancer Database (NCDB). Methods: Patients (pts) with clinical stage T1b-2N0 and any pathological stage (excluding metastatic) adenocarcinoma of the esophagus, GEJ, and stomach treated with neoadjuvant therapy or upfront surgery, with or without adjuvant chemotherapy (AC), were identified between 2004 and 2015 in the NCDB. Univariate and multivariable analyses were conducted, and Kaplan-Meier analysis and Cox proportional hazard models were used to identify the association between the three treatment modalities and overall survival (OS). Results: A total of 2260 pts were analyzed. The median follow-up was 66.6 months. The median age was 67 years. Most pts were White (86%) and male (77%). 1018 (45%) had moderately-differentiated grade, while 946 (42%) had poorly-differentiated/undifferentiated grade. The most common site of disease was the lower third of esophagus (34.1%). 161 pts (7%) received NACT, of whom 45 pts received AC; 537 pts (24%) received NACRT, of whom 40 pts received AC. 1562 pts (69%) underwent US, of whom 146 pts received AC. US with AC was associated with the best survival, followed by NACT with AC; median OS was 90.1 and 86.8 months for surgery with AC and NACT with AC, respectively. NACRT was associated with the worst survival (39.5 and 40.2 months with and without AC, respectively). The 5-year OS rates were 59.8%, 58.5%, 52.1%, 44.9%, 37.3%, and 37.8%, for US, NACT, and NACRT, with and without AC, respectively. The rate of tumor upstaging was highest in the NACT group, followed by the NACRT group, and lowest in the US group. Postsurgically, 62 (39%) and 48 (30%) pts in the NACT group and 198 (37%) and 161 (30%) pts in the NACRT group had upstaging in their T and N stages, respectively, compared to 214 (13%) and 326 (21%) pts in the US group. For the 1107 pts who also had pathological T1b-2N0 stage disease following US, no difference in survival was observed with or without AC. Conclusions: Upfront surgery with adjuvant chemotherapy and perioperative chemotherapy are associated with the best survival compared to preoperative radiotherapy. This is the largest study to address the best approach for the treatment of T1b-2 stage disease.

35 Background: The combination of oxaliplatin, bolus 5-FU (b5FU), infusional 5-FU (5-FUCI), and leucovorin (LV) is the preferred first line treatment option for mCRC. This study evaluates the impact of b5FU on survival in first line therapy for mCRC patients treated with mFOLFOX6. Methods: This was a retrospective chart review of patients ≥ 18 years old with mCRC receiving palliative first line mFOLFOX6 chemotherapy with or without b5FU/ LV from January 1, 2010 through June 1, 2019 at Winship Cancer Institute, Emory University. Data collection included the following: demographics (age, race, gender), disease characteristics (tumor sidedness), microsatellite status, KRAS status, BRAF status, addition of monoclonal antibodies (bevacizumab, panitumumab), ECOG PS, grade 3/4 neutropenic events, addition of growth factors, and treatment delays. The primary endpoint was PFS. The multivariable Cox proportional hazards model for PFS and OS was performed with selected covariates of interest. Results: A total of 252 patients with mCRC met the inclusion criteria. Median follow-up time was 2.4 years. 161 patients (64%) received mFOLFOX6 with b5FU/LV and 91 patients (36%) received mFOLFOX6 with no b5FU/LV. More cycles were delivered in the b5FU group as compared to the non-b5FU group (mean, 4.8 v. 3.8 cycles, respectively; p < 0.001). There were no differences in grade 3 and 4 neutropenic events between groups. Growth factor usage was numerically higher in the bolus group though not significantly different (p = 0.06). No difference was observed in treatment delays between groups (p = 0.83). There was no statistical difference in PFS between treatment groups (1.1 years in the b5FU/LV group v. 0.8 years (95% CI, 0.6-1.0) in the no 5-FU/LV bolus group; p = 0.076). The median OS was 2.5 years in the b5FU/LV group compared to 1.8 years in the no b5FU/LV group (p = 0.012). On univariate analysis, tumor sidedness and performance status were significantly different between groups. On multivariate analysis, none of the variables were significantly different between groups. Conclusions: The omission of the b5FU/LV from mFOLFOX6 does not significantly impact PFS, toxicity or treatment delays. However, OS is significantly shorter when the b5FU/LV is omitted suggesting the clinical importance of maintaining bolus administration with 5-FUCI in the first line palliative treatment of mCRC.

125 Background: Pathologic staging in colorectal cancer (CRC) is crucial in patient management. Data regarding the impact of size/horizontal tumor extent is limited, contradictory and currently excluded from the American Joint Committee on Cancer (AJCC) staging model. However, a previously published SEER analysis showed that AJCC stages I and IIIA have similar 2- and 5- year survival rates, and worse rates for stage II. Using the largest cohort to date, we report the impact of primary tumor size on CRC survival. Methods: Data were obtained from all US hospitals that contributed to the National Cancer Database (NCDB) between 2010 and 2015. Univariate and multivariate analyses were performed to identify factors associated with patient outcome. Kaplan-Meier analysis and Cox proportional hazards models were used to assess the association between tumor/patient characteristics and overall survival (OS). Results: A total of 61,145 patients were identified with a similar gender distribution (M/F:50.9%/49.1%). The mean age was 62.7years (SD+/-14.1) and 82% were non-Hispanic Whites. Majority had colon primary (82.7%) and 82.4% had microsatellite stable (MSS) disease. Distribution across stages I-IV was 20.1%, 32.1%, 34.7% and 13.2% respectively. Among the total study population, AJCC stage correlated closely with OS on multivariate analysis (HR 1.49, 2.29, 8.38 for stages II to IV compared to stage I), while the distinguishing power for tumor size was relatively mild (HR 1.19 and 1.33 for 5-10 cm and >5cm compared to 10cm were associated with worse survival compared to those 10cm (HR 1.57; 1.37-1.80; p

TPS153 Background: The clinical benefit of approved therapies in patients (pts) with metastatic colorectal cancer (mCRC) who progress on first- and second-line chemotherapy (FOLFOX and FOLFIRI) is limited. In pts with chemotherapy-refractory RAS wild type mCRC, antibodies targeting EGFR offer a monotherapy response rate of approximately 20% and a progression-free survival (PFS) of 4 months (Price 2014). HER2 is a validated target in gastric and breast cancers, with HER2 amplification occurring in ~3–5% of pts with mCRC. Tucatinib (TUC), recently approved for HER2+ metastatic breast cancer, is a tyrosine kinase inhibitor (TKI) highly selective for HER2 with minimal inhibition of EGFR. In pt-derived xenograft models of HER2+ mCRC, the combination of TUC + trastuzumab (TRAS) showed significantly greater antitumor activity compared with either agent alone (Kulukian 2020). The MOUNTAINEER trial was initiated to evaluate the efficacy and safety of TUC in combination with TRAS in pts with HER2+ RAS wild-type mCRC. Interim analysis of the initial 26 pts enrolled in MOUNTAINEER demonstrated an objective response rate (ORR) of 52.2% (12 partial responses [PRs] in 23 evaluable pts), median duration of response of 10.4 months, with a median PFS of 8.1 months and a median overall survival (OS) of 18.7 months (Strickler 2019). Based on these results, the trial was expanded to enable better estimation of ORR and safety. Methods: MOUNTAINEER (NCT03043313) is an open-label, pivotal phase 2 trial that initially consisted of a single cohort of up to 45 pts (Cohort A) treated with TUC (300 mg BID) and TRAS (8 mg/kg IV followed by 6 mg/kg IV every 3 weeks). The trial was expanded to include an additional 70 pts randomized 4:3 into 2 cohorts: Cohort B (N = 40) who will receive TUC + TRAS, and Cohort C (N = 30) who will receive TUC monotherapy. Pts in Cohort C will be treated with TUC (300 mg orally twice daily) with the option to crossover to TUC + TRAS if an objective response is not achieved by 12 weeks, or if progressive disease develops at any time. Eligible pts have RAS wild-type and HER2+ mCRC, and must have previously received regimens that include fluoropyrimidines, oxaliplatin, irinotecan, anti-VEGF therapy, and an anti-PD-1 if the tumor has dMMR proteins or is MSI-H. Pts who have received prior HER2-directed therapies are not eligible. Additionally, pts must have measurable disease and ECOG PS of 0 to 2. The primary endpoint of this trial is confirmed ORR (per RECIST v1.1) in Cohorts A + B as assessed by blinded independent central review. Secondary endpoints include duration of response, PFS, OS, and safety and tolerability. Enrollment is ongoing in the US and planned for the EU. Clinical trial information: NCT03043313.

95 Background: Preclinical data suggests metformin can improve immune exhaustion of tumor infiltrating lymphocytes and potentiate the effects of PD-1 blockade. By normalizing the hypoxic TME, metformin was shown to improve cytotoxic T cell function and efficacy of anti-PD-1 antibody in highly aggressive B16 melanoma and MC38 colon adenocarcinoma tumor models. Based on this preclinical rationale we conducted a phase II study with nivolumab and metformin combination in treatment refractory MSS metastatic colorectal cancer (mCRC). Methods: Nivolumab 480 mg IV every 4 weeks and Metformin 1000 mg po twice daily was administered in 28-day cycles following a 14-day metformin only lead-in phase.Eligible patients included stage IV metastatic treatment refractory MSS mCRC (patients must have received oxaliplatin, irinotecan, and fluoropyrimidine), age ≥18 years, ECOG PS 0-1, adequate organ function, no prior anti PD-1 agent. The primary endpoint was overall response rate (ORR). Secondary endpoints included overall survival (OS) and progression free survival (PFS). Simon’s two-stage Minimax design was employed (H0: ORR =4%; H1: ORR=15%; alpha = 0.1; power =80%). If ≥1 objective response was observed in the first evaluable 18 patients, 10 additional patients would be included in the cohort. ≥3 objective responders in 28 patients would be required to be considered positive study. Pre-treatment and on-treatment research biopsies and correlative peripheral blood specimens were collected. Results: A total of 24 patients were enrolled, 6 patients were replaced per protocol, and 18 patients had evaluable disease. Of the 18 evaluable patients 11/18 (61%) were female, median age 58 [IQR 50-67]. 2 patients had prolonged stable disease (4 and 10 cycles). No patients had objective response based on RECIST 1.1. Median OS and PFS was 5.1 months [95% CI (2-11.7)] and 2.3 months [95% CI (1.7-2.4)], respectively. Most common grade 3 and 4 toxicities were anemia (n=2) and diarrhea (n=2). Conclusions: In treatment refractory MSS mCRCnivolumab and metformin combination was well tolerated. Two patients achieved stable disease, but no objective response was seen; therefore, the study did not proceed with the second stage of enrollment. Immunologic correlative analysis of this study is ongoing. Clinical trial information: NCT03800602.

Background The survival impact of multi-agent (MAC) compared with single-agent (SAC) adjuvant chemotherapy (AC) in elderly patients with stage III colon cancer (CC) remains controversial. The aim of this study was to compare survival outcomes of MAC and SAC in this population utilizing the National Cancer Database (NCDB). Patients and Methods Patients aged ≥70 years with pathological stage III CC diagnosed in 2004-2015 were identified in the NCDB. Univariate and multivariable analyses were conducted, and Kaplan-Meier analysis and Cox proportional hazard models were used to identify associations between MAC vs. SAC and overall survival (OS). Results Among 41 707 elderly patients (≥70 years old) with stage III CC, about half (n = 20 257; 48.5%) received AC; the majority (n = 12 923, 63.8%) received MAC. The median age was 79 (range 70-90). The majority were female (n = 11 201, 55.3%), Caucasians (88%) and had moderately differentiated tumor grade (n = 12 619, 62.3%), tumor size >4 cm (11 785, 58.2%), and negative surgical margins (18 496, 91.3%). Low-risk stage III CC constituted 50.6% (n = 10 264) of the study population. High-risk stage III CC was associated with worse OS compared with low-risk disease (HR 0.35, 0.34-0.36, P < .001). Multi-agent chemotherapy was associated with a better 5-year OS compared with SAC (P < .001). High-risk stage III patients who received MAC vs. SAC had an OS of 4.2 vs. 3.4 years, respectively (P < .001). Low-risk stage III patients who received MAC vs. SAC had a median OS of 8.5 vs. 7 years (P < .001). In univariate and multivariable analyses, male sex, positive surgical margin, insurance and facility types, age, year of diagnosis, tumor size, and Charlson-Deyo score of >2 were associated with worse OS (P < .05). Conclusions Any adjuvant chemotherapy has a trend of survival benefits. Multi-agent chemotherapy seems to have an enhanced benefit in the 70-75 age group. Multi-agent chemotherapy seemed to have similar efficacy as SAC in those aged >76 years.

TPS143 Background: Patients with KRAS and NRAS ( RAS) wild-type mCRC benefit from the epidermal growth factor receptor (EGFR) monoclonal antibodies (Abs) panitumumab and cetuximab, but nearly all patients experience resistance. Blood-based profiling of cell free DNA (cfDNA) can identify genomic alterations that drive acquired EGFR Ab resistance. After discontinuation of anti-EGFR Abs, acquired genomic alterations decay over time to undetectable levels. Some studies have suggested clinical benefit from EGFR Ab rechallenge, but there is limited evidence that EGFR Ab rechallenge improves survival compared to standard of care (SOC) therapies. We hypothesize that cfDNA profiling will identify patients appropriate for panitumumab rechallenge, and that these molecularly selected patients will have improved survival compared to current SOC therapies. Methods: This is a randomized phase II, open label study designed to compare the overall survival (OS) of panitumumab rechallenge versus SOC (investigator choice TAS-102 or regorafenib). Secondary objectives include comparisons of progression free survival, objective response rate, clinical benefit rate, and quality of life as measured by the linear analogue self-assessment (LASA) questionnaire. Eligible patients have radiographically measurable KRAS, NRAS, and BRAF codon 600 wild-type mCRC based on tumor tissue testing, and must have experienced progression or intolerance to treatment with a fluoropyrimidine, oxaliplatin, irinotecan, an anti-VEGF Ab, and an anti-PD-1 Ab if the tumor has mismatch repair deficiency or is MSI-H. Progression after at least 4 months treatment with an anti-EGFR Ab is required. All patients must be enrolled in the COLOMATE cfDNA screening protocol (NCT03765736) and meet molecular eligibility based on Guardant360 cfDNA profiling (absence of amplification of ERBB2, KRAS, NRAS, and MET; absence of mutations of BRAF, EGFR, ERBB2, KRAS, NRAS, and MET [mutant allele frequency > 0.5%]). Greater than 90 days must have elapsed between the most recent treatment with an anti-EGFR Ab and cfDNA profiling. Dosing for all study drugs is according to clinical SOC. 120 patients will be randomized 1:1 to panitumumab rechallenge or SOC. With 83 OS events, this study will have 80% power to detect an improvement in median OS from 6.5 to 10 months (HR=0.65; 1-sided α= 0.15). This study began enrollment in 6/2020. Recruitment is ongoing at 16 sites in the Academic and Community Cancer Research United (ACCRU) network (ACCRU-GI-1623). Clinical trial information: NCT03992456.

7079 Background: Pain is a common symptom of cancer, affecting patients' function and quality of life. It is also a common cause of hospitalization for cancer patients. The aim of this study was to evaluate the cost of in-hospital pain management among US cancer patients. Methods: A retrospective analysis of data from all US hospitals that contributed to the National Inpatient Sample for 2011-2015 was conducted. All cancer patients admitted for pain management were included in the analysis. Main outcomes were factors significantly associated with hospital length of stay, total charge per hospital stay, and in-hospital mortality. Weighted chi-square test was used for categorical covariates and univariate analysis was performed using a logistic model. Results: 122,776 patient discharges were identified. Mean age was 59.3 years and 52.3% were female. 65.9% stayed in the hospital for longer than 72 hours, with a median total hospital charge of $48,156. Conversely, the median total hospital charge for those spending less than 72 hours on admission was $15,966. Median total charge per hospital stay was similar among insured and uninsured/self-pay patients ($32,879 vs. $32,323; p=0.013), but higher in patients without metastatic disease ($33,315 vs. $29,369; p

4583 Background: Resected cholangiocarcinomas are rare and have high relapse rates. Adjuvant chemotherapy is the standard of care (BiLCAP Trial). Adjuvant radiation therapy benefit is not well defined. This study aims to evaluate survival outcomes of the effect of adjuvant chemoradiotherapy compared to chemotherapy in extrahepatic cholangiocarcinoma (EHC) using the National Cancer Database (NCDB). Methods: Patients with resected EHC between 2004 and 2013 were identified from the NCDB using ICD-O-3 histology and topography codes: 8140, 8160, 8161, 8162 and C24.0. Patients with neoadjuvant therapy were excluded from this analysis. Univariate and multivariable analyses were conducted, and Kaplan-Meier Curves were used to compare overall survival (OS) based on treatment received. Results: A total of 236 EHC patients were identified. Males comprised 60.6% and 88.1% were Caucasian. Median age was 64 (range, 31-84) years. The majority were distal (72.0%, N = 157) followed by perihilar (20.6%, N = 45), hilar (6.4%, N = 14) and cystic (0.9%, N = 2). Distribution across stages I-III was 28.8% (N = 68), 56.8% (N = 134), and 14.4% (N = 34), consecutively. Adjuvant chemotherapy was given in 37.7% (N = 89) and adjuvant chemoradiotherapy in 62.3% (N = 147). The median dose of radiation was 50.4 Gy. Adjuvant chemoradiotherapy was mostly given in regional node positive disease (p = 0.016) and negative surgical margin (p = 0.002) compared to regional node negative disease and positive surgical margin, respectively. The use of adjuvant chemoradiotherapy was associated with improved OS compared to chemotherapy alone in univariate (HR 0.64; 95% CI 0.44-0.93; p = 0.019) and multivariable analysis (HR 0.65; 95% CI 0.44-0.96; p = 0.030). Median survival and 1 year-OS for patients that received chemoradiotherapy was 33.8 months (95% CI 28, NA) and 87.7% (80.9%, 92.1%) compared to chemotherapy alone which was 23.8 months (95% CI 18.9, 35.4) and 75.5% (64.9%, 83.3%). Conclusions: Adjuvant chemoradiotherapy was associated with improved survival in patients with resected EHC compared to chemotherapy alone. This conclusion warrants further prospective studies to confirm these results.

TPS3163 Background: Regulatory T cells (Treg) can dampen anti-tumor immune responses in the tumor microenvironment (TME). The predominant chemokine receptor on human Treg is CCR4, the receptor for the chemokines CCL17 and CCL22, which are produced by tumor cells, tumor-associated macrophages and dendritic cells, as well as by effector T cells (Teff) in the setting of an inflammatory anti-tumor response. Preclinical studies with orally-available CCR4 antagonists have demonstrated potent inhibition of Treg migration into tumors, an increase in the intratumoral Teff/Treg ratio, and anti-tumor efficacy as a single agent and in combination with checkpoint inhibitors. In a first-in-human trial conducted in healthy volunteers, the oral CCR4 antagonist FLX475 was demonstrated to be well tolerated with outstanding PK properties. A robust PD assay measuring receptor occupancy on circulating Treg demonstrated the ability to safely achieve exposure levels predicted to maximally inhibit Treg recruitment into tumors via CCR4 signaling. These human PK, PD, and safety data have enabled a streamlined design of a Phase 1/2 study of FLX475 in cancer patients both as monotherapy and in combination with checkpoint inhibitor. Methods: This clinical trial is a Phase 1/2, open-label, dose-escalation and cohort expansion study to determine the safety and preliminary anti-tumor activity of FLX475 as monotherapy and in combination with pembrolizumab. The study is being conducted in 2 parts, a dose-escalation phase (Part 1) and a cohort expansion phase (Part 2). In Part 1 (Phase 1) of the study, at least 3 to 6 eligible subjects are being enrolled in sequential cohorts treated with successively higher doses of FLX475 as monotherapy (Part 1a) or in combination with pembrolizumab (Part 1b). In Part 2 (Phase 2) of the study, expansion cohorts of both checkpoint-naïve and checkpoint-experienced patients with tumor types predicted to be enriched for Treg and/or CCR4 ligand expression (i.e. “charged tumors”) -- including both EBV+ and HPV+ tumors and NSCLC, HNSCC, and TNBC -- will be enrolled using a Simon 2-stage design. As of February 4, 2020, Phase 1 dose escalation has been completed and a recommended Phase 2 dose chosen for both FLX475 monotherapy and combination therapy with pembrolizumab. Enrollment into Phase 2 expansion cohorts has been initiated. Clinical trial information: NCT03674567 .

553 Background: Sarcopenia and inflammation are independently associated with worse survival in cancer patients. This study aims to determine the impact of inflammatory biomarkers, BMI and sarcopenia on survival in advanced hepatocellular carcinoma (HCC) patients treated with immunotherapy. Methods: We performed a retrospective review of advanced HCC patients treated with immunotherapy-based therapies at Winship Cancer Institute between 2015 and 2019. Baseline computed tomography and magnetic resonance imaging scans were collected at mid-L3 level, assessed for skeletal muscle density using SliceOmatic (TomoVision, version 5.0) and converted to skeletal muscle index (SMI) by dividing it by height (m)2. Gender-specific sarcopenia was defined by median value of SMI. The optimal cut for continuous inflammation biomarker was determined by bias-adjusted log-rank test. Overall Survival (OS) was set as primary outcome and Cox proportional hazard model was performed. Results: 57 patients were included; 77.2% male, 52.6% Caucasian, 58.5% ECOG PS 0-1, 80.7% Child Pugh A. Treatment was second line and beyond in 71.9%. The median follow-up time was 6 months. Sarcopenia cut-off for males and females was SMI of 43 and 39, respectively. 49.1% of patients had sarcopenia. Median OS was 5 vs. 14.3 months in sarcopenic vs. non-sarcopenic patients (p=0.054). Median OS was 5 and 17.5 months in patients with BMI

TPS269 Background: Panitumumab (Pmab) is a recombinant monoclonal antibody that binds specifically to the human epidermal growth factor receptor (EGFR), and is indicated for metastatic colorectal carcinoma (mCRC). EGFR inhibition induces synthetic lethality with poly ADP ribose polymerase inhibitors (PARPi) by attenuating DNA repair pathways. This susceptibility to PARPi-induced cell death by EGFR inhibition is associated with deficient Non-homologous end joining (NHEJ), and Homologous recombination (HR) mediated DNA repair and persistence of DNA damage. Furthermore, efficacy of PARPi (such as niraparib) is highly correlated with platinum sensitivity. Cancer cell sensitivity and resistance to both PARPi and platinum have been associated with loss and restoration of HR DNA repair, indicating similar mechanisms of anticancer activity and resistance. Platinum sensitivity in CRC could therefore predict for anticancer properties of PARPi when utilized in the setting of synthetic lethality. Combining PARP and EGFR inhibition has the potential to confer synergistic benefit, while ameliorating resistance mechanism to PARPi. This study aims to evaluate the activity of the combination of niraparib and Pmab in RAS wildtype (WT) mCRC. Methods: Eligible patients for the trial include advanced, RAS WT mCRC who have been intolerant of, progressed on, or failed at least one line of systemic chemotherapy. Those currently on first line oxaliplatin-containing regimen are allowed on the trial if they have remained stable or better (PR or CR) for at least 4 months on that line of treatment, and are being considered for maintenance therapy as standard of care. Patients must also be 18 years old, ECOG PS 0-1 and measurable disease per RECIST 1.1. A safety run-in cohort of 6 eligible patients, and additional 20 patients with the same inclusion criteria will be enrolled. Pmab dose - 6 mg/kg IV on days 1 & 15 of each 28-day cycle; Niraparib - 200mg or 300mg (based on body weight and platelet count) orally continuously. Primary endpoint: clinical benefit rate (CR +PR + SD). Biomarker analysis includes skin biopsies evaluated for p-Caspace-3, PARP, p-MAPK, Ki-67, and p27. The study was activated in Sept. 2019. Clinical trial information: NCT03983993.

830 Background: XL888 is a selective inhibitor of heat shock protein 90 (HSP90). It modulates several oncogenic signaling pathways, and the tumor microenvironment. In preclinical models, XL888 potentiates efficacy of PD-1 inhibition. We report the results of the dose escalation (DE) portion of a phase Ib trial of combined XL888 and pembrolizumab (P) in advanced gastrointestinal adenocarcinomas. Methods: XL888 was administered orally (PO) in three dose levels of 45 (DL1), 90 (DL2), 60 (only if DLT on DL2) mg twice weekly with P 200 mg IV on day 1, in 21-day cycles. Eligible patients included stage IV or locally advanced unresectable gastrointestinal adenocarcinomas with at least one prior therapy (patients with colorectal (CRC) adenocarcinoma must have received oxaliplatin, irinotecan, and fluoropyrimidine), age ≥18 years, ECOG PS 0-1, adequate organ function, no prior anti-PD-1 or anti-PD-L1 agent. The primary endpoint was recommended phase II dose (RP2D), while secondary endpoints included safety and tolerability. Pre-treatment and on-treatment correlative peripheral blood specimens were collected. Results: A total of 14 patients were enrolled in the DE phase. 9 male, median age 66.5. Diagnoses included CRC (6), pancreatic adenocarcinoma (5), biliary tract cancer (1), ampullary (1), and duodenal (1). Two patients were ineligible for assessing the primary endpoint (DL2) due to biliary stent obstruction and sepsis. One DLT (grade 3 autoimmune hepatitis) was observed on DL2. We enrolled three patients on DL3. Five additional patients were subsequently enrolled on DL2 with no additional DLT. Three patients (1 duodenal, 2 CRC) had prolonged stable disease (6, 9 and 15 cycles). The most common treatment-related toxicities included autoimmune hepatitis (G3; n = 1), retinopathy (G2; n = 2), nausea (G2; n = 1), constipation (G2; n = 1), and diarrhea (G2; n = 3). Conclusions: The XL888 and pembrolizumab combination had an acceptable safety profile and the RP2D of XL888 was 90 mg twice weekly combined with P 200 mg, every 3 weeks. The dose expansion portion and a robust series of immunologic correlative laboratory studies for this study is ongoing. Clinical trial information: NCT03095781.

703 Background: Locally advanced pancreatic cancer (LAPC) is managed with multimodality therapy. A subset of patients with LAPC are not good candidates for aggressive treatment. The aim here is to evaluate the outcomes of single modality radiation therapy for LAPC using the National Cancer Database (NCDB). Methods: Data was obtained between years 2004 and 2013. Pancreatic ductal adenocarcinoma (PDAC) patients with unresectable local disease were identified excluding patients who received chemotherapy or surgery. Univariate and multivariable analyses identified factors associated with patient outcome. Kaplan-Meier analysis and Cox proportional hazards models were used for patient characteristics and overall survival (OS). Results: A total of 6,590 patients were included; 480 (6.9%) received radiation therapy only and 6470 (93.1%) received no treatment. Mean age was 73.5 (range, 28‐90) years, with the majority being White (N = 5685; 83.2%) and female (N = 3779; 54.4%). Poorly differentiated histology and tumors ≥ 4 cm ( > T3 stage) accounted for 47.8% and 52.7%, respectively. The median dose of radiation was 39.6 Gy. Stereotactic body radiation (SBRT) was given in 64 patients and external-beam/Intensity modulated radiotherapy (IMRT) in 416 patients. Charlson-Deyo score of +1 was seen in 34.4% of patients who received no treatment, 32.8% of patients who received SBRT and in 29.8% of patients who received external-beam IMRT. Radiation therapy was associated with improved OS compared to no treatment in univariate and multivariable analyses controlling for sex, Charlson-Deyo score, age, tumor size, amongst other covariates. Median OS for patients who received SBRT, external-beam/IMRT or no radiation was 8.6, 6.7 and 3.4 months; respectively (P < 0.001). There is a significant difference in 12-month OS for the SBRT cohort (31.9%; 95% CI 20.9%-43.5%) compared to patients who received no radiation (15.1%; 95% CI 14.2%-16.0%), similarly seen on multivariable analysis (HR 0.50; 95% CI 0.38-0.65; P < 0.001). Conclusions: The current study is the first to evaluate the efficacy of radiation as single modality therapy in LAPC. The results suggest a potential benefit for radiation therapy alone, in comparison to no treatment.

Background: Clinico-pathological high-risk features are frequently utilized in adjuvant chemotherapy (AC) decisions in stage II colorectal cancer and their utility in stage II appendiceal adenocarcinoma (AA) is not established. The aim of this study is to determine the impact of high-risk features in clinical outcomes and whether high risk features are predictive of AC benefit in stage II AA. Methods: Patients with pathological stage II AA between 2010-2015 were identified from the National Cancer Database (NCDB) using ICD-O-3 morphology and topography codes: 8140, 8480 and C18.1. High risk stage II AA was defined as having at least one of the following clinicopathological features: T4 tumor, Results: A total of 1,040 patients with pathological stage II AA were identified. 51.0% males, 84.5% Caucasian; median age 61 (range, 19-90). 46.4% were determined to have high-risk stage II AA. High-risk status was associated with worse OS compared to low-risk in univariate (HR 1.55; 95% CI 1.18-2.02; p=0.001) and multivariable analyses (HR 1.36; 95% CI 1.03-1.79; p=0.028). High-risk stage II AA patients had significantly worse 5-year OS compared to low-risk patients (67.1% vs. 74.5%, p=0.0013). AC was administered in 34.4% (n=166) of high-risk patients and in 36.5% (n=203) of low-risk patients. Among high-risk patients, AC was not associated with better OS in univariate (HR 0.86; 95% CI 0.59-1.26; p=0.448) and multivariable analyses (HR 1.35; 95% CI 0.90-2.04; p=0.151) compared to no AC. Similarly, among low-risk patients, AC was not associated with better OS in univariate (HR 0.92; 95% CI 0.60-1.39; p=0.679) and multivariable analyses (HR 1.27; 95% CI 0.81-2.02; p=0.299) compared to no AC. For high-risk patients, 5-year OS was 68.3% in patients that received AC vs. 66.5% in patients that did not (p=0.722). For low-risk patients, 5-year OS was 74.0% in patients that received AC vs. 76.3% in patients that did not (p=0.813).Conclusion: High-risk stage II AA patients had significantly worse 5-year OS compared to low-risk patients. AC did not improve survival regardless of high-risk features in stage II AA.

796 Background: Goblet cell tumors (GCT) of the appendix are very rare tumors constituting 2.5%-5% of all primary appendiceal neoplasms. Role of adjuvant chemotherapy (AC) is not established for GCT. This study aims to evaluate the impact of AC in stage II-III appendiceal GCT. Methods: Patients with pathological stage II and III GCT who underwent surgical resection between 2006 and 2015 were identified from the National Cancer Database (NCDB) using ICD-O-3 morphology and topography codes: 8243/3, 8245/3 and C18.1. Patients treated with neoadjuvant systemic and/or radiation therapy and adjuvant radiation were excluded. Univariate and multivariable analyses were conducted, and Kaplan-Meier Curves were used to compare overall survival (OS) based on treatment received with Log-rank test. Results: A total of 1,046 patients were identified. 53.7% males and 89.0% Caucasian; median age 56 (range, 20-90) years. Distribution across pathological stages II-III was 83.6% (N = 874) and 16.4% (N = 172) consecutively. 8.3% (N = 73) of stage II and 50.6% (N = 87) of stage III patients received AC. In the total cohort, AC was not associated with better OS compared to no AC in univariate analysis (HR 1.84; 95% CI 1.26-2.67; p = 0.001) or multivariable analysis (HR 0.94; 95% CI 0.57-1.52; p = 0.790). For stage II patients, AC was not associated with better OS in univariate (HR 1.24; 95% CI 0.60-2.57; p = 0.562) or multivariable analyses (HR 1.67; 95% CI 0.76-3.64; p = 0.199). Similarly, in stage III patients, AC was not associated with better OS in univariate (HR 0.78; 95% CI 0.48-1.29; p = 0.340) or multivariable analyses (HR 0.55; 95% CI 0.28-1.04; p = 0.067). In the entire cohort 5-year OS for patients that received AC was 83.9% (80.3%, 86.9%) versus 70.7% (60.9%, 78.5%) (p = 0.001) with no AC. For stage II patients, 5-year OS was 77.3% with AC vs. 87.7% with no AC (p = 0.562). For stage III patients, 5-year OS was 64.8% with AC vs. 54.4% with no AC (p = 0.340). Conclusions: AC was not associated with improved 5-year OS in patients with pathological stage II and III GCT compared to no AC.

e15029 Background: ICIs induce durable responses in dMMR CRC pts with overall response rates (ORR) of 30-50%. Even though the loss of expression of any MMR gene predicts ICIs response, it is unknown if ORRs are similar across all MMR genes (MLH1, PMS2, MSH2, and MSH6). In this study, we analyzed the impact of each specific MMR gene loss and clinical characteristics of pts with best response to ICIs. Methods: Pts were eligible if they had confirmed dMMR CRC by IHC or microsatellite instability-high (MSI-H) by PCR, and received ICIs between 01/01/2012 and 10/01/2018 at Winship Cancer Institute of Emory University, Mayo Clinic or Vanderbilt University Medical Center. Due to the pattern of frequent concurrent loss and functional dependency, the groups were categorized as MLH1 ±PMS2 vs. MSH2 ±MSH6. Cox proportional hazard model and Fisher’s exact test were used for the best response and the distribution of variable among the subgroups. Results: A total of 45 pts with dMMR CRC were identified. ORRs in MLH1 ±PMS2 and MSH2 ±MSH6 groups were 68% and 57.1% respectively without statistical difference (Table). Pts with age < 50 and 50-65 years old had better ORRs compared to pts with age >65 (58.3%, 85.7% and 42.1% respectively, P=0.036). Left-sided tumors had a trend toward higher ORRs compared to right-sided tumors (83.3% vs 51.5% P=0.086). Gender and BRAF status were not predictors of response. BRAF mutations were more common in right-sided tumors (29.6% vs 11.1% respectively) and in older patients. Conclusions: Our data suggest that MSI-H CRC pts aged 50-65 treated with ICIs, have improved ORR compared to pts > 65; pts with left-sided tumors have a trend toward improved ORR compared to those with right sided tumors. [Table: see text]

4110 Background: Neuroendocrine tumors (NET) comprise around 2% of all malignant tumors of the gastrointestinal system. The genomic landscape of NET has not been well studied. The aim of this study was to confirm the feasibility of next generation sequencing (NGS) using ctDNA in NET and characterize common alterations in the genomic profile. Methods: Molecular alterations in 114 plasma samples from 114 patients with NET using clinical-grade NGS of ctDNA (Guardant360Ò) across multiple institutions were evaluated. The test detects single nucleotide variants in 54-73 genes, copy number amplifications, fusions, and indels in selected genes. Results: A total of 114 NET patients were evaluated, of which 64 (56.1%) were female. Mean age was 59.7 years with a range between 23-89 years. ctDNA NGS testing was performed on 114 plasma samples; 1 patient had testing performed twice. Genomic alterations were defined in 94 (n = 94/114, 82.5%) samples with a total of 289 alterations identified after excluding variants of uncertain significance (VUSs) and synonymous mutations. Alterations were identified in at least one sample from 83 patients; TP53 associated genes were most commonly altered (n = 83/289, 28.7%), followed by KRAS (n = 22, 7.6%), PI3CA (n = 15, 5.2%), CCNE1 (n = 15, 5.2%), BRAF (n = 13, 4.5%), MYC (n = 12, 4.1%), ERBB2 (n = 11, 3.8%), APC (n = 10, 3.5%), EGFR (n = 10, 3.5%), MET (n = 10, 3.5%), PTEN (n = 9, 3.1%), RB1 (n = 9, 3.1%), CDK6 (n = 7, 2.4%), AR (n = 5, 1.7%), ARID1A (n = 5, 1.7%), FGFR1 (n = 5, 1.7%), and PDGFRA (n = 5, 1.7%). Other genomic alterations of low frequency, but clinical relevance included: CDK4 (n = 4, 1.3%), NF1 (n = 4, 1.3%), RAF1 (n = 4, 1.3%), GNAS (n = 3, 1.0%), KIT (n = 3, 1.3%), BRCA2 (n = 2, 0.7%), CCND2 (n = 2, 0.7%), CTNNB1 (n = 2, 0.7%), JAK2 (n = 2, 0.7%), NRAS (n = 2, 0.7%), SMAD4 (n = 2, 0.7%), and TERT (n = 2, 0.7%). Alterations in AKT1, ALK, ATM, BRCA1, CCND1, CDKN2A, FGFR2, MTOR, RHOA, SMO and STK11 were all reported once (n = 1, 0.3%). Conclusions: Evaluation of ctDNA is feasible among individuals with NET. Liquid biopsies are not invasive and can provide personalized options for targeted therapies in NET patients.

e15693 Background: Resection of the primary tumor in metastatic neuroendocrine tumor (NET) is controversial. The aim of this study is to evaluate survival outcomes and identify prognostic variables of surgical resection of the primary tumor in metastatic NET patients. Methods: Data were obtained from all US hospitals that contributed to the National Cancer Database (NCDB) between 2004 and 2013. Chi-square and ANOVA tests were done to identify factors associated with surgical modality. Univariate and multivariate cox proportional hazards models were used for association between patient characteristics and survival. Kaplan-Meier curves were generated and log-rank tests conducted to compare the survival difference of patient characteristics. Results: A total of 2,361 patients between 18 and 90 years of age with stage IV well/intermediate-differentiated NET were identified. The mean age was 62.1 years (SD±13), with an equal male to female ratio (50.0%). Majority of NET primaries were in the small intestine (33.0%), pancreas (26.3%), and lung (24.4%). The majority were well differentiated tumors (69.6%) and 42.5% of patients underwent surgery at the primary site. On multivariate analysis total surgical resection of the primary (HR 0.44; 0.22-0.90; p < 0.001), female sex, year of diagnosis 2010-2014, negative surgical margin, Charlson-Deyo score < 2, and age < 51 years at diagnosis were associated with better overall survival (OS). Conclusions: Resection of the primary in stage IV well/intermediate-differentiated NET was associated with improved 5-year OS compared to patients with no surgery in small intestine (60.1% vs 44.2%), lung (70.0% vs 20.2%), and pancreas tumors (59.3% vs 30.6%).

4116 Background: Despite the therapeutic promise of ICIs for patients (pts) with some advanced malignancies, they are FDA-approved for only a few GI cancer pts. In NSCLC, melanoma and urothelial carcinoma, there is emerging data that pts who experience IRAEs while on ICIs have improved outcomes compared with pts who do not. This association in GI cancer pts has not been reported. Methods: We retrospectively analyzed outcomes for metastatic GI cancer pts receiving ICIs for FDA-approved indications (later-line MSI-H tumors, 2nd line hepatocellular carcinoma (HCC), 3rd line PD-L1+ gastric (GA)/gastroesophageal junction (GEJ) adenocarcinoma), at Vanderbilt Ingram Cancer Center, Winship Cancer Institute and Stanford Cancer Institute. Our primary aim was to compare progression-free survival (PFS) and overall survival (OS) between pts who did and did not experience IRAEs. Secondary aims were comparison of these outcomes within pts who experienced IRAEs, by initial IRAE severity (Grade (G)3/G4 vs G1/G2) (CTCAE v5.0), time-to-onset (TTO) (≤ 6 weeks (w) vs > 6 w) and management (steroids vs drug cessation vs observation). PFS and OS were determined by Kaplan-Meier (KM) analysis; KM comparisons were done by the logrank test. Results: Between 1/2015-12/2018 61 GI cancer pts with HCC (28), colorectal cancer (27) and GA/GEJ cancer (6) were treated with ICIs; median age was 63 years. The majority (59) received single-agent nivolumab or pembrolizumab while minority (2) received nivolumab and ipilimumab; median time on ICIs was 5.9 months (mos). Twenty-four pts experienced initial IRAEs (6 G3/G4, 18 G1/G2); median TTO was 3.8 mos. Pts who experienced any IRAE had improvements in PFS and OS compared to those who did not (PFS: 32.4 mos (95% confidence interval (CI), 32.4-not reached (NR)) vs 4.8 mos (95% CI, 2.9-8.7), p = 0.0001; OS: 32.4 mos (95% CI, 32.4-NR) vs 8.5 mos (95% CI, 6-NR), p = 0.0036). Among pts who experienced IRAEs, PFS and OS differences between above-specified subgroups did not meet statistical significance. Conclusions: GI cancer pts who experienced IRAEs while on ICIs had marked improvements in PFS and OS compared to those who did not, suggesting the predictive potential for IRAEs as a clinical biomarker in this population.

e18231 Background: Knowledge about perioperative systemic therapy in metastatic colorectal cancer (mCRC) is limited. We aim to describe the nationwide pattern of use and survival outcomes of patients with mCRC treated with surgical resection. Methods: Data were obtained from all US hospitals that contributed to the National Cancer Database (NCDB) between 2004 and 2013. Univariate and multivariate analyses was done to identify factors associated with patient outcome. Results: A total of 61,940 patients with stage IV CRC older than 18 years were identified. Mean age was 63.4 years (SD±14), with a male preponderance (54.8%). About 80% were Caucasian and 69.9% had colon cancer. Compared to medical treatment only, resection of both primary and metastatic sites (13.5%; HR 0.40; 0.37-0.44; p < 0.001), or primary site resection alone (49.2%; HR 0.52; 0.48-0.56; p < 0.001) were associated with improved overall survival (OS). Other co-variates associated with improved survival included younger age group, year of diagnosis (2009-2013), colon tumor location, and < 3 metastatic sites (Table). Five-year OS for resection of primary and metastatic site (28.2%) was higher than for primary site resection alone (14.9%) or no surgical treatment (4.7%). Conclusions: Resection of metastatic sites or primary tumor was associated with improved survival in patients with stage IV CRC.[Table: see text]

560 Background: Although clinical outcomes has substantially improved over the last decade, long term survival in mCRC remains rare. Molecular profiling (MP) of CRC is routinely conducted to identify potential therapeutic targets. The aim of this project is to evaluate the impact of uncommon GAs on outcomes and characterize their distribution by age. Methods: Pts were eligible if they had mCRC (synchronous or metachronous) and underwent MP between 01/2013 and 05/2018. GAs were obtained from Foundation Medicine reports. Clinical data were collected by trained personnel by detailed chart review. Multivariable survival analyses (MA) with Cox model were conducted for survival outcomes and Fisher’s exact test was used to assess the differences among age groups (< 45, 45-60, > 60). The study was reviewed by Institutional IRB ( IRB00097021 ). Results: 161 patients with mCRC had MP, and 159 of those patients had survival data. The most commonly detected GAs were APC (133/161, 82.6%) TP53 (128/161, 79.5%). In univariate analyses mutations in BRCA 1/2, RB1, SOX9, CDK8, FLT3, and IRS2 amplification were associated with worse survival outcomes. In MA, including initial stage of disease, GAs in BRCA1/2, RB1, FLT3, SOX9, and IRS2 remained statistically significant (Table). When we performed MA by age groups, mutations SOX9 in age group < 45 and BRCA1/2 in age group 45-60 were significant predictors of worse outcomes. We also compared the frequency of mutations among age groups and FAM123B was significantly more common in age group 45-60 (P = 0.038). Conclusions: Our data suggests that GAs in BRCA1/2, RB1, FLT3, SOX9, and IRS2 may predict worse outcomes in mCRC. Therapeutic approaches targeting these pathways should be investigated. Differences in distribution and prognostic significance of mutations were observed based on age. [Table: see text]

658 Background: Appendiceal cancers (AC) comprise around 0.5% of all gastrointestinal neoplasia. The genomic landscape of AC has not been well studied. The yield of circulating tumor DNA (ctDNA) from the plasma of patients with AC has not been reported. The aim of this study is to confirm the feasibility of NGS using ctDNA and characterize common alternations in the genomic profile of AC. Methods: The molecular alterations in 372 plasma samples from 303 patients with AC using clinical-grade NGS of ctDNA (Guardant 360) across multiple institutions, was evaluated. The test detects single nucleotide variants in 54 -73 genes, copy number amplifications, fusions, and indels in selected genes. Results: A total of 303 AC patients were evaluated; 169 female (56%). Median age was 56.8 (range: 25-83). ctDNA NGS testing was done on 372 plasma samples; 48 patients had testing performed twice, 9 three times, and 1 was tested four times. Genomic alterations were defined in 207 (55.6%) samples with a total of 288 alterations identified after excluding variants of uncertain significance (VUSs) and synonymous mutations. TP53 associated genes were most commonly altered (n = 96, 33.3%), followed by KRAS (n = 41, 14.2%), APC (n = 19, 6.6%), EGFR (n = 15, 5.2%), BRAF (n = 13, 4.5%), NF1 (n = 13, 4.5%), MYC (n = 9, 3.1%), GNAS (n = 8, 2.7%), PI3CA (n = 7, 2.4%), MET (n = 6, 2.08%), ATM in 6 (1.6%). Other genomic alterations of low frequency, but clinically relevant: AR (n = 4, 1.39%), TERT (n = 4, 1.39%), ERBB2 (n = 4, 1.39%), SMAD4 (n = 3, 1.04%), CDK4 (n = 2, 0.69%), NRAS (n = 2, 0.69%), FGFR1 (n = 2, 0.69%), FGFR2 (n = 2, 0.69%), PTEN (n = 2, 0.69%), RB1 (n = 2, 0.69%), and CDK6, CDKN2A, BRCA1, BRCA2, JAK2, IDH2, MAPK, NTRK1, CDH1, ARID1A, and PDGFRA were all reported once. Conclusions: Evaluation of ctDNA was feasible among individuals with AC. The frequency of genomic alterations in ctDNA testing is similar to those previously reported in tissue NGS. Liquid biopsies are non-invasive methods that can provide personalized options for targeted therapies in patients with AC.

435 Background: There is no consensus regarding treatment for HCC variants. Clinical outcomes of HCC variants differ from pure HCC. The aim of this study is to compare clinicopathological characteristics, treatment, and outcomes of HCC variants with pure HCC. Methods: Patients with HCC and variants with 8170/3-8175/3 and 8180/3 ICD-O-3 codes were identified from National Cancer Database between 2004 and 2013. Univariate and multivariate survival analyses were conducted to analyze the association between histology and overall survival (OS). Results: 80,280 patients were identified; pure HCC 78,461 (97.7%), fibrolamellar (FLHCC) 310 (0.4%), scirrhous 161 (0.2%), spindle cell 72 (0.1%), clear cell 487 (0.6%), pleomorphic 23 (0.0%), and combined HCC and cholangiocarcinoma (mixed HCC) 766 (1.0%). 76.7% were male and 72% Caucasian. The mean age was similar in all except FLHCC (37.9 vs. 60.9-64.1 years, p < 0.001). Liver transplant was performed in 10.1% of pure HCC, 14.5% of mixed HCC, 16.2% of scirrhous, 6.9% of spindle cell, 8.8% of clear cell, 8.7% of pleomorphic, and 3.2% of FLHCC (p < 0.001). Pure HCC (10.57%) underwent surgical resection less often than variants; FLHCC (54.8%), clear cell (34.5%), mixed HCC (29.8%), spindle cell (33.3%), pleomorphic (34.8%), and scirrhous (9.9%) (p < 0.001). Ablation was performed in 9.8% of pure HCC, and in up to 8.7% of HCC variants. More than a third of all patients received chemotherapy; pure HCC (42.3%), mixed HCC (38.5%), scirrhous (31.1%), spindle cell (36.1%), clear cell (35.5%), pleomorphic (34.8%), and FLHCC (41.3%). FLHCC had the best 5-year OS (38.7%), spindle cell and pleomorphic had the worst (9.6% and 13.0%). In univariate and multivariate analyses, fibrolamellar histology, female sex, diagnosis between 2009 and 2013, treatment at academic center, well/moderately differentiated histology, early stage, and chemotherapy was associated with better OS compared to pure HCC, male sex, diagnosis between 2004 and 2008, treatment at community cancer program, poorly differentiated, late stage, and no chemotherapy (p < 0.001). Conclusions: HCC variants underwent surgical resection more often than HCC. FLHCC had the best 5-year OS. Liver transplant is commonly performed in HCC variants.

TPS4155Background: Trifluridine/tipiracil (FTD/TPI, also known as TAS-102) is a combination of a nucleoside analogue and a thymidine phosphorylase inhibitor. TAS-102 has shown activity in 5FU-resis...

TPS2617Background: LYC-55716 is a first-in-class, oral, small-molecule agonist of the retinoic acid receptor–related orphan receptor γ (RORγ) under development as a novel immuno-oncology agent for ...

3604Background: Randomized phase III trials have shown that patients with dMMR/ MSI-H stage II colon cancer (CC) do not benefit from adjuvant chemotherapy. However, a subgroup of stage II patients ...

e16190Background: Pegfilgrastim (Pg), a long-acting G-CSF used to prevent neutropenia, is not indicated for administration within 24 hrs of completion of chemotherapy. The safety of administering P...

e15022Background: Ideal biomarkers for cancer pts receiving IO are currently lacking. Neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), and platelet-to-lymphocyte ratio (PLR...

e16262Background: Small bowel adenocarcinomas (SBA) are rare tumors. Management of SBA is extrapolated from colorectal cancer treatments. Recent evidence suggests that the biology and molecular fea...

421 Background: High grade neuroendocrine tumors of the gastrointestinal tract are rare tumors. Management strategies are modeled after small cell lung cancer (SCLC). Treatment patterns and outcomes have not been studied. Methods: Data were obtained from all US hospitals that contributed to the National Cancer Database (NCDB) between 2004 and 2013. Univariate and multivariate testing was done to identify factors associated with patient outcome. Kaplan-Meier analysis and Cox proportional hazards models were used to assess the association between patient characteristics and survival. Results: A total of 1,861 patients were identified for the 10 years of the study. The mean age was 63 years (SD±13), with a male preponderance (53.3%). The vast majority of patients (78.1%) were non-Hispanic Whites. The most common primary sites were pancreas (PNET = 19.4%), large intestine (18.1%), esophagus (17.8%) and rectum (15.5%). About 27.9% of the cases were resectable at the time of diagnosis, and distribution across stages 1-IV was 6.6%, 10.5%, 18% and 64.6% consecutively. Liver was a common site of metastases (50.4%), followed by bone (11.3%) and lungs (10.8%). Only 3.5% of the patients had brain metastases. On univariable analysis, age < 65years (HR 0.72; 0.66-0.8; p < 0.001) and treatment at an academic center (HR 0.88; 0.79-0.99; p < 0.034) were associated with improved survival. Multivariable analysis confirmed prognostic advantage of treatment at an academic center. Patients treated with chemotherapy had a median overall survival (OS) of 11.2 months, compared with 1.7 months for those who did not. The median OS for high grade PNET was 6 months, compared to 9.9 months for other HG-GI-NETs. One year and 5-year survival rates were 27.5% vs. 41% and 4.5% vs. 12.3% respectively. Conclusions: This is the largest series of HG-GI-NET. Almost two-thirds of the cases present with metastatic disease. Pattern of metastasis differs from SCLC. Survival is short. Treatment at high volume academic center, younger age and use of chemotherapy are associated with improved survival.

TPS526 Background: Heat shock protein 90 (HSP90) has a central role in modulating tumor microenvironment, inflammatory signaling pathways (NF-κB, HIF-1α and Jak-STAT), tumor antigen presentation and expression, PD-L1 expression and macrophage migration inhibitory factor (MIF) as well as cytokine production. Inhibitors of HSP90 have been shown in preclinical studies and in patient samples to exert anti-tumor effects and modulate signaling pathways. XL888 is a selective inhibitor of HSP90. Based on this preclinical rationale, we have developed a phase Ib/II trial to determine the recommended phase II dose, evaluate the safety, toxicity profile, preliminary antitumor activity, and immunogenicity of the XL888 and Pembrolizumab combination in previously treated patients with advanced gastrointestinal tumors. Methods: The phase Ib trial design is standard 3+3. XL888 is administered orally (PO) in three dose levels of 45 (DL1), 90 (DL2), 60 (only if DLT on DL2) mg twice weekly with pembrolizumab at 200 mg IV on day 1, in 21-day cycles. Eligible patients must have stage IV or locally advanced unresectable gastrointestinal adenocarcinomas who have failed at least one prior therapy (patients with colorectal adenocarcinoma must have previously received oxaliplatin, irinotecan, and fluoropyrimidine), age ≥18 years, ECOG PS 0-1, no prior anti PD-1 or anti-PD-L1 agent. After recommended phase II dose is established, an expansion phase will enroll 16 patients with pancreatic adenocarcinoma (Arm A) and 16 patients with colorectal adenocarcinoma (Arm B). Primary endpoint response rate. In the expansion phase patients will receive initial cycle (3 weeks) treatment with either pembrolizumab or pembrolizumab plus XL888 and then starting cycle 2 all patients receive the combination. Blood will be collected pre-treatment, post 1st and 2nd cycle. Eight patients in each arm will undergo pre and post treatment tumor biopsies. This design will enable us to evaluate the effects of pembrolizumab alone versus the combination. This study was activated in June 2017 and to date 4 patients were enrolled in dose escalation phase. The dose expansion phase is expected to start accrual in December 2017. Clinical trial information: NCT03095781.

406 Background: Survival of resectable pancreas cancer (RPC) treated with resection and adjuvant therapy is 22-28 months (mo). Locally advanced unresectable pancreatic cancer (LAPC) treated with combination chemotherapy have a median survival of 24 mo. The objective of this project is to evaluate the effect of neoadjuvant treatment on survival outcome of localized PC. Methods: Charts of localized PC patients treated at Emory University from 2009 to 2016 were reviewed. Information on demographics, stage and treatment was collected. Survival rates were estimated by Kaplan-Meier method and compared with log-rank test. A Cox proportional hazard model was fitted to estimate the adjusted effect of treatment on overall survival(OS). Results: A total of 415 patients were included; 144 RPC, 158 borderline resectable (BRPC) and 108 LAPC. Stage was determined at the multidisciplinary conference. The median age was 67.7 years (30-92); 49% male, and 63% Caucasians. The median OS for RPC, BRPC, and LAPC was 16.9, 14.6 and 10.9 mo, respectively. Stage, type of chemotherapy and age were significant predictors of OS after adjusting for gender, race, age, surgery, stage, chemotherapy, margins and radiation. Of the 144 RPC, 137 underwent surgery and 3 received neoadjuvant treatment; 73 RPC were followed in outside facility with missing follow up data. Of the 71 RPC treated at Emory; 91% received adjuvant gemcitabine. Of the 158 BRPC, 84 underwent surgery; 44 received FOLFIRINOX neoadjuvant therapy, 23 received gemcitabine/nab-paclitaxel, and 16 received gemcitabine single agent. BRPC patients who underwent resection had a median OS of 18.5 mo (95%CI: 14.2, 26.4), significantly longer than RPC (P = 0.044). Combination chemotherapy was significantly associated with improved OS at 36 mo (38.9%) when compared to single agent gemcitabine (6.3% at 36 mo) (p = 0.009). BRPC patients who received FOLFORINOX and surgery had a median OS of 31.5 mo. Conclusions: Overall survival of BRPC patients who undergo resection after FOLFIRINOX is significantly improved (more than doubled) compared to upfront resection for RPC. Preoperative therapy provides the best approach for systemic disease early in the course of treatment.

3612 Background: The RAS/RAF/MEK signal transduction pathway is critical to the development of colorectal cancer, and tumors harboring KRAS, NRAS, and BRAF mutations were shown to be resistant to radiation. Thus, we conducted a phase I study of trametinib, a potent MEK1/2 inhibitor, in combination with CRT in patients with LARC. Methods: Phase I trial for patients with Stage II/III rectal cancers with a 3+3 design, and an expansion cohort of 12 patients at the maximum tolerated dose (MTD). Trametinib is given orally at 3 dose levels: 0.5mg, 1mg, and 2mg (Mon-Fri). CRT regimen is infusional 5-flourouracil (5FU) 225mg/m2/day (Mon-Fri) and daily fractions of 1.8 Gy (total 50.4Gy). There is a 5-day trametinib lead-in followed by trametinib and CRT. Six to 10 weeks after completion of CRT, patients then proceed to their surgery and adjuvant therapy. The primary endpoint is to identify the MTD and recommended phase 2 dose of trametinib with CRT. Immunohistochemistry staining for phosphorylated –ERK (pERK) and genomic profiling is performed on the tumor samples. Results: Enrollment is complete at all dose levels with18 patients, and 15 patients evaluable for toxicity and response as of Feb 6. One dose-limiting toxicity of diarrhea was observed at the 2mg dose. Grade 3 and most common toxicities are shown in Table 1. No grade 4/5 toxicities have been observed. At 2mg dose level, 3/9 (33%) patients had pathological complete response (pCR) and 2/9 (22%) had a near pCR. Correlative studies confirm decrease in pERK levels with increasing doses of trametinib. Correlation of genomic mutational status with toxicity, response, and outcomes is being analyzed. Conclusions: The combination of trametinib with 5FU CRT is tolerable with promising preliminary activity. Final results will be presented at the meeting. Toxicities. Clinical trial information: NCT01740648. [Table: see text]

TPS3624 Background: To improve survival for patients with mCRC, efforts are needed to identify and treat actionable genomic alterations. HER2 is amplified in approximately 5-8% of patients with KRAS and NRAS (RAS) wild-type mCRC. HER2 functions as an oncogenic driver and a mediator of EGFR antibody (Ab) resistance. Although prior studies have shown that anti-HER2 therapies are active in patients with HER2+ (HER2 IHC 3+ or HER2 amplified) mCRC, there are no HER2-directed therapies approved for these patients. Tucatinib is a potent and highly selective oral small molecule tyrosine kinase inhibitor of HER2, currently being developed to treat metastatic breast cancer. In HER2+ CRC patient derived xenograft models, tucatinib has substantial anti-tumor activity. The addition of the anti-HER2 monoclonal Ab trastuzumab augments tumor growth inhibition. Methods: This single-arm phase II study will test the combination of tucatinib and trastuzumab in patients with HER2+ mCRC. Eligible patients include those with RAS wild-type mCRC who have been previously treated with 5-FU, oxaliplatin, irinotecan, and an anti-VEGF monoclonal Ab. Patients must have HER2+ disease by IHC, FISH, or NGS. Prior treatment with anti-HER2 targeting therapy is excluded. The primary objective is to assess the objective response rate for the combination. Secondary objectives are to evaluate the efficacy (PFS, OS, clinical benefit rate), safety, and tolerability of the combination. Correlation between tissue and blood-based biomarkers and clinical outcomes will be explored. Blood will be collected at baseline and each restaging to determine if the combination eliminates HER2 amplified circulating tumor DNA. Subjects will receive tucatinib at a dose of 300mg by mouth daily, and trastuzumab will be administered every 3 weeks (8 mg/kg IV day 1 of cycle 1, then 6 mg/kg IV Q3 weeks). Response will be assessed every 3 cycles (9 weeks) per RECIST version 1.1. Both agents will be provided by the study. This study was initiated in February 2017. Recruitment is ongoing at 8 sites in the Academic and Community Cancer Research United (ACCRU) network. Clinical trial information: NCT03043313.

e15168 Background: 2-8% of all colorectal cancer (CRC) cases are in younger adults (YAs), patients (pts) less than age 50. However, current understanding of CRC in YAs is inadequate, especially that of sporadic onset. We conducted a study to describe the landscape of genomic alterations in YA CRC pts presenting to a large academic practice. Methods: Adult pts with CRC presenting to The Ohio State University Comprehensive Cancer Center oncology clinics were offered next generation sequencing (NGS) through a customized 22-gene Ion AmpliSeq Mutation Panel as part of clinical care. Commonly mutated areas of select genes (including AKT1, ALK, BRAF, EGFR, ERBB2/4, FBXW7, FGFR1/2/3, KRAS/NRAS, MET, NOTCH1, PIK3CA, PTEN, TP53) were sequenced from tumor sections. Institutional review board approval was obtained to retrospectively analyze this NGS testing between 1/2013-3/2016. Results: 258 CRC pts underwent genomic profiling. 57 pts (22.1%) were YAs at diagnosis (range 22-49 years); 20 pts (7.8%) were 40 years old or younger. 31 YA pts (54.4%) had metastatic disease. Of the YAs with CRC, 18 pts (31.6%) were diagnosed with R-sided colon, 16 pts (28.1%) with L-sided colon, and 22 pts (38.6%) with rectal cancer. 110 genomic alterations were found in YA pts, with a mean of 1.9 mutations per tumor (range 0-6); 35 (31.8%) of these in 32 (56.1%) YA pts were actionable. Of these 110 alterations, 41.8% were in TP53, 28.2% in KRAS/NRAS, 10.0% in PIK3CA, 3.6% in BRAF, 3.6% in FBXW7, and 2.73% in PTEN. 6 YA pts (10.5%) had microsatellite instability (MSI-H). Only 1 pt had concomitant MSI-H and a BRAF mutation; 4 pts with BRAF mutations were microsatellite stable. Comparing our YA pts to a separate cohort of pts age > 50 who had testing done, no significant difference was seen in mutation incidence in KRAS/NRAS (p = 1.0), TP53 (p = 0.3), PIK3CA (p = 0.128), or BRAF (p = 1.0). Conclusions: Genomic profiling through a targeted NGS panel is feasible as part of routine clinical practice. There is disagreement in the literature on genetic mutations in YA compared to older age CRC pts. Knowledge of the genomic landscape in YAs with CRC will lead to improved understanding of the underlying biology of CRC in YAs as it differs from CRC in older pts, and could impact future care of this cohort.

TPS3629 Background: Improvements in outcomes for locally advanced rectal cancer (LARC) have plateaued due to an inability to consistently deliver adjuvant therapy (tx) and thus far ineffective novel therapies. Systematic testing of new chemotherapy and radiation sensitizers are needed to advance treatment outcomes. This randomized phase II modular clinical trial platform utilizes Total Neoadjuvant Therapy (TNT) with parallel experimental arms in LARC. The experimental arms are not intended for direct comparison, but to test a variety of sensitizers or hypotheses in a consistent and relatively homogenous high-risk patient (pt) population with correlative biomarkers. Success of any given experimental arm will be determined by achievement of pathologic endpoints compared to a control arm. Methods: This NCTN multi-arm randomized phase II trial serves as a modular platform to assess novel sensitizers to neoadjuvant chemotherapy and/or chemoradiotherapy (chemoRT) in LARC. Eligibility includes LARC as defined by any ONE of the following criteria: distal location (cT3-4 ≤5cm from the anal verge, any N); bulky (any cT4 or tumor within 3mm of the mesorectal fascia); high risk for metastatic disease (cN2); or not a candidate for sphincter-sparing surgical resection. After randomization, pts receive neoadjuvant FOLFOX x 4mo → chemoRT (capecitabine with 50.4Gy) → surgical resection 8-12 wks later. Based on promising phase I results, the first experimental arm will assess the activity of veliparib added to standard chemoRT (capecitabine + RT). Primary endpoint is to demonstrate improvement in Neoadjuvant Rectal Cancer (NAR) score for the experimental arm vs control representing 20% relative risk reduction in DFS HR and 3-4% absolute OS improvement. Secondary endpoints include comparisons of OS, DFS, toxicity, pCR, cCR, tx completion, negative surgical margins, sphincter preservation, sphincter function including quality of life, and exploratory assessments of molecular and radiographic predictors of response and distant failure. Target accrual is 79 evaluable pts per arm with additional arms added through rolling protocol amendments. NCT02921256. Support: U10 CA-180868, -20, 21, -22; UG-189867; AbbVie. Clinical trial information: NCT02921256.

6559 Background: The incidence of colorectal cancer (CRC) in young adults is increasing. Minority populations with CRC are known to have worse outcome. The objective of this study is to evaluate the impact of race on the outcome of young adults with CRC. Methods: Data were obtained from all US hospitals that contributed to the National Cancer Database (NCDB) between 2004 and 2013. Univariate and multivariate testing was done to identify factors associated with patient outcome. Kaplan-Meier analysis and Cox proportional hazards models were used for association between patient characteristics and survival. Results: A total of 83,449 patients between 18 and 50 years of age were identified. The mean age was 43.6 years (SD±6), with a male preponderance (53.9%). About 72% were non-Hispanic Whites (NHW) while African Americans (AA) made up 15.1%. Distribution across stages I-IV was 15.6%, 22.4%, 33.9% and 27% consecutively, similar among the races. 41.8% of NHW and 28.4% of AA had rectal cancers (p

e18069 Background: Pancreatic cancer is a disease of the elderly. The treatment and outcomes of young adults with pancreatic cancer has not been well studied. The aim of this study is to describe the treatment, outcomes, and impact of race in young adults with pancreatic cancer. Methods: Data were obtained from all US hospitals that contributed to the National Cancer Database (NCDB) between 2004 and 2013. Univariate and multivariate testing was done to identify factors associated with patient outcome. Kaplan-Meier analysis and Cox proportional hazards models were used to assess the association between patient characteristics, time intervals and survival. Results: A total of 9,657 patients between 18 and 50 years of age were identified. The mean age was 45.4 years (SD±4.6), with a male preponderance (58.3%). Distribution across stages I-IV was 6.1%, 31.1%, 13.9% and 48.8% consecutively, and was similar across all racial groups. About 30.9% of patients underwent resection of the primary pancreatic tumor. Univariate analysis showed survival difference between ages 18-34 vs. 35-50 years old (HR 0.81; 0.71-0.92; p

685 Background: RAS/BRAF mutations constitutively activate the MAPK pathway in colorectal cancer, and may promote resistance to CRT. We propose that trametinib, a MEK1/2 inhibitor, in combination with 5FU CRT for patients with LARC will improve outcome. Methods: Phase I study with standard 3+3 design in patients with Stage II/III rectal cancer with 3 dose levels of trametinib: 0.5, 1, and 2mg daily with 5FU 225mg/m2/day and 50.4 Gy. Trametinib was given over a 5-day lead-in and continued through the course of CRT. Patients undergo surgery 6-10 weeks after the completion of CRT. An expansion cohort at the maximum tolerated dose (MTD) with 12 patients is ongoing. Tumor tissue is collected prior to therapy, at day 4/5 of trametinib, and at surgery. The primary endpoint is to determine the MTD of trametinib with CRT. Results: 15 patients (10 males, 5 females) have been enrolled and 14 patients are evaluable for toxicities to date. Median age is 53 years (range 35-74). Patients have completed enrollment to all dose levels, with 1 dose-limiting toxicity of diarrhea attributed to 5FU CRT. No grade 4/5 toxicities, and toxicities are shown in the table. Generalized skin rash led to trametinib discontinuation after 2 weeks of therapy for 1 patient, and was held 3 days for 2 patients. At the trametinib dose level of 2mg, 3 out of 7 (43%) patients had a pathological complete response and the average neoadjuvant rectal (NAR) score is 8.1. Tumor RAS/BRAF mutation status is determined. Analysis of tumor tissue shows dose-dependent decrease in phosphorylated-ERK1/2 with increasing doses of trametinib. Conclusions: Initial evaluation shows that the combination of trametinib with 5FU CRT is tolerable and effective, and warrants further investigation in LARC. Clinical trial information: NCT01740648. [Table: see text]