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TPS296 Background: AZD5305 is a potent and selective oral PARP inhibitor (PARPi) that specifically targets and traps PARP1, in contrast to approved PARPis which target both PARP1 and PARP2. Preclinical data suggest that PARP1 inhibition confers antiproliferative effects, while PARP2 inhibition is a major driver of hematological toxicity. Thus, AZD5305 may have an improved therapeutic index with less toxicity. The Phase 3 PROpel study showed that first-line olaparib plus abiraterone (abi) significantly improved radiographic progression-free survival (rPFS) over abi alone in pts with metastatic castration-resistant prostate cancer (mCRPC) enrolled irrespective of homologous recombination repair (HRR) gene mutations (Clarke et al, NEJM Evidence 2022). There is a need for better understanding of the benefit of adding PARPi to NHA and the potential synergy between them in early treatment of mPC. The PETRANHA study (NCT05367440) is evaluating the combination of AZD5305 with physician’s choice of NHA including abi, darolutamide, and enzalutamide, in pts with mPC. Methods: This is a multi-arm, open-label, nonrandomized dose-escalation phase study. Key eligibility criteria include age ≥18 years, histologically confirmed mPC (mCRPC or metastatic castration-sensitive prostate cancer [mCSPC], suitability for NHA treatment, ECOG PS 0–1, and life expectancy ≥16 wks. HRR gene mutation status is assessed at screening by testing blood, tumor or circulating tumor (ct) DNA; however, an identified mutation is not required for study entry. Key exclusion criteria for pts with mCRPC include previous PARPi, platinum chemotherapy, or targeted radioligand therapy. For pts with mCSPC, key exclusion criteria are the same, plus previous NHA or docetaxel in the mCSPC setting. Treatment continues until disease progression, starting an alternative anticancer therapy, or unacceptable toxicity. The primary objectives are to assess the safety and tolerability of AZD5305 in combination with NHAs, in terms of adverse events (AEs), serious AEs, and dose-limiting toxicities. Key secondary objectives include characterization of pharmacokinetics, changes in tumor size and prostate-specific antigen level, and assessment of preliminary antitumor activity by objective response rate, rPFS, and time to and duration of response by RECIST v1.1 and Prostate Cancer Clinical Trials Working Group 3 criteria. Exploratory endpoints include evaluating the role of predictive biomarkers including longitudinal assessment of ct cells and ctDNA, prostate-specific membrane antigen positron emission tomography (PET) and fluorodeoxyglucose PET. Enrollment began on June 23, 2022, in Melbourne, Australia; additional sites are planned in Australia, USA, and Europe. Clinical trial information: NCT05367440 .

2505 Background: Immunoglobulin-like transcript 3 (ILT3) is an inhibitory receptor associated with immune tolerance and T-cell suppression within the tumor microenvironment. MK-0482, a novel humanized IgG4 mAb targeting ILT3, is undergoing phase 1 evaluation ± pembrolizumab (pembro) in advanced solid tumors (NCT03918278; MK-0482-001). Dose escalation data are presented. Methods: Eligible patients with advanced solid tumors were enrolled into sequentially escalating dose cohorts of MK-0482 monotherapy (0.2-2250 mg) or MK-0482 (7.5-2250 mg) + pembro 200 mg; both were administered IV Q3W for up to 35 cycles or until progressive disease (PD), unacceptable toxicity, death, or withdrawal. Patients receiving MK-0482 monotherapy could cross over to MK-0482 + pembro after PD. Primary objectives were safety, tolerability, and determination of the recommended phase 2 dose (RP2D). Secondary and exploratory objectives included assessing pharmacokinetics (PK), blood receptor occupancy (RO), anti–drug antibodies (ADA), and objective response rate (ORR) per RECIST v1.1 by investigator assessment. Results: Seventy-five patients were enrolled (n = 29, MK-0482 monotherapy; n = 46, MK-0482 + pembro); 8 patients crossed over to receive the combination. Median age was 63 years (range, 34-86); 73% had ECOG PS 1, 72% received ≥2 lines of prior anticancer therapy, and 32% received prior PD-1/PD-L1 inhibitors. Treatment-related AEs (TRAEs; any-grade/grade 3 or 4) were reported in 34%/7% of patients with MK-0482 monotherapy, 67%/4% with MK-0482 + pembro, and 50%/13% in those who crossed over. The most common TRAEs (≥10% of all patients) were pyrexia (10%) with MK-0482 monotherapy; fatigue (24%) and arthralgia, diarrhea, hyperthyroidism, hypothyroidism, and pruritus (11% each) with MK-0482 + pembro; and arthralgia (25%), hyperthyroidism and hypothyroidism (13% each) for patients who crossed over. Dose-limiting toxicities occurred in 2 patients who received MK-0482 + pembro: 1 grade 5 myositis (MK-0482 750 mg; the only TRAE leading to death) and 1 grade 2 myositis (MK-0482 2250 mg). Preliminary PK and blood RO data suggested that target-mediated drug disposition of MK-0482 was likely saturated in blood mononuclear cells at doses ≥75 mg. ADA to MK-0482 was observed in ̃20% of patients, but no clear impact on MK-0482 PK was observed. A confirmed ORR of 15% (8 PR) was observed in patients who received MK-0482 + pembro, including patients who crossed over; no confirmed responses were observed in patients who received MK-0482 monotherapy. MK-0482 750 mg + pembro was selected as the RP2D based on the totality of data. Conclusions: MK-0482 ± pembro was generally well tolerated, and combination therapy provided modest antitumor activity in patients with heavily pretreated advanced solid tumors. The RP2D of MK-0482 + pembro is under further evaluation in tumor-specific cohorts. Clinical trial information: NCT03918278.

2560 Background: Strong preclinical rationale supports combining checkpoint inhibition (CPI) with T cell costimulatory agonists, particularly of CD28, a critical T cell costimulatory molecule recognized as a key target of checkpoint inhibition. Davoceticept (ALPN-202) is a variant CD80 vIgD-Fc fusion that mediates PD-L1-dependent CD28 costimulation and inhibits the PD-L1 and CTLA-4 checkpoints. It has demonstrated superiority to CPI-only therapies in multiple tumor models in vitro and in vivo, while demonstrating favorable preclinical safety. Methods: This is an open-label dose escalation and expansion study of davoceticept in adults with advanced solid tumors or lymphoma (NCT04186637). Patients with cancers refractory to standard therapies including CPIs, or cancers without available standard or curative therapy are eligible. Dose escalation studied two dose schedules, Q1W and Q3W. Objectives include safety and tolerability, PK, PD and preliminary anticancer activity. Disease assessments are evaluated by RECIST v1.1 for solid tumors. A prior presentation discussed the first 5 cohorts of the Q1W schedule; this presentation updates progress in dose escalation, including the Q3W schedule. Results: As of January 2022, 57 adults with various advanced solid tumors, most commonly colorectal and pancreatic, received davoceticept monotherapy, which was well tolerated through 10 mg/kg Q3W. It demonstrated dose-dependent PK and target saturation. Immune-related AEs (irAEs), occurred in 20/57 (35%), mostly of the skin, endocrine and gastrointestinal systems. All but 4 of the irAE were grade 1-2. Only one DLT (chronic active gastritis grade 3) was observed at 3 mg/kg Q3W. Among 48 evaluable patients, unconfirmed partial responses were observed in 2 (colorectal and renal cell). Stable disease, at first scan at 6 weeks, was observed in 23 (48%); 11 (23%) demonstrated volume reduction (target lesion ΔSLD < 0%); 2 had SD for > 6 months, and 1 had an ongoing SD at 8 months. At doses above 0.1 mg/kg, ex vivo analyses showed agonism of T cell CD28, and flow cytometry demonstrated increased circulating activated (ICOS+), proliferating (Ki-67+) and central memory T cells, and reduced regulatory T cells, consistent with CD28 engagement. Conclusions: Davoceticept was well tolerated at doses capable of engaging CD28 costimulation in vivo, with early signs of activity and peripheral immune activation in a largely treatment-refractory, non-immunogenic tumor population. These findings support an additive benefit of combining CD28 agonism with checkpoint inhibition and identify biologically active dose regimens of davoceticept for subsequent single agent development, and provide further rationale for combination study. Expansion cohorts, including cutaneous melanoma and PD-L1-positive cancers, are planned, and a combination study with pembrolizumab has initiated (NCT04920383). Clinical trial information: NCT04186637.

434 Background: Combination of anti-VEGF compounds and immune checkpoint inhibitors is an approved therapy across multiple solid tumors, including advanced HCC. This phase Ib study (NCT03468426) is assessing BI 836880 (bispecific VEGF/Ang2 nanobody) + ezabenlimab (anti-PD-1 antibody) in pts with advanced solid tumors. The recommended phase 2 dose (RP2D) of BI 836880 720 mg + ezabenlimab 240 mg given IV every 3 weeks was determined in Part 1. In Part 2, RP2D was assessed in 7 expansion cohorts. We report data from cohorts in HCC after prior sorafenib/lenvatinib (cohort F) and untreated unresectable HCC (cohort G). Methods: Pts with locally advanced or metastatic HCC, Child-Pugh class A, not eligible for surgical or locoregional therapies were enrolled. Cohort F enrolled pts who had progressed on or after first-line treatment with sorafenib or lenvatinib or who had discontinued due to poor tolerability after ≥2 weeks of treatment. Cohort G enrolled pts who had received no prior systemic therapy for HCC. Treatment continued until disease progression, undue toxicity or consent withdrawal. Primary endpoint is objective response rate (ORR) by RECIST 1.1. Results: As of Aug 2021, 30/31 pts have been treated in cohorts F/G: 87/77% male; median age 65/64 yrs. Follow-up is ongoing in both cohorts. 9/19 pts in cohorts F/G remain on treatment; median (range) duration of treatment is 175 (42–532)/ 169 (42–336) days in cohorts F/G. All pts were evaluable for response in cohort F: confirmed ORR to date is 40% (1 complete response; 11 partial responses [PRs]). Of 28 evaluable pts in cohort G, confirmed ORR to date is 21% (6 PRs). 12 (40%) pts in cohort F and 18 (64%) in cohort G have stable disease. In cohort F, AEs were reported in 28 (93%) pts, most frequently hypertension and proteinuria (each 30%). In cohort G, AEs occurred in 26 (84%) pts, most frequently ascites (26%) and thrombocytopenia (19%). 24 (80%) pts in cohort F and 15 (48%) in cohort G had treatment-related AEs (TRAEs). Most frequent TRAEs were proteinuria (27%), infusion-related reactions (IRRs) and hypertension (each 20%) in cohort F, and hypertension (13%), IRRs, hypothyroidism and diarrhea (each 10%) in cohort G. There were 3 pts with G5 AEs in cohort F (COVID-19 pneumonia [n = 1]; low Glasgow coma score and dyspnea [n = 1]; hepatic cirrhosis [n = 1]) and 1 G5 AE in cohort G (hepatic failure); none were considered related to treatment. AEs leading to discontinuation occurred in 2 pts in cohort F (G3 hepatic encephalopathy and G2 duodenal ulcer) and 3 in cohort G (G5 hepatic failure [n = 1]; G2 acute kidney injury and G1 decreased appetite [n = 1]; G2 diarrhea [n = 1]). Conclusions: BI 836880 + ezabenlimab had a manageable safety profile and showed promising activity in pts with untreated and second-line post-sorafenib/lenvatinib advanced HCC. Data continue to mature, particularly in cohort G. Cohort F has been expanded by a further 30 pts. Clinical trial information: NCT03468426.

2547 Background: Strong preclinical rationale has emerged for combining checkpoint inhibition (CPI) with T cell costimulatory agonists, particularly CD28, a critical T cell costimulatory molecule recently recognized as a key target of checkpoint inhibition. ALPN-202 is a variant CD80 vIgD-Fc fusion that mediates PD-L1-dependent CD28 costimulation and inhibits the PD-L1 and CTLA-4 checkpoints. It has demonstrated superiority to CPI-only therapies in tumor models, while demonstrating favorable safety in preclinical toxicology studies. Methods: This is a cohort-based, open-label dose escalation and expansion study of ALPN-202 in adults with advanced solid tumors or lymphoma (NCT04186637). Subjects with cancers refractory to standard therapies (including approved CPIs), or cancers without available standard or curative therapy are eligible. After two planned single-subject cohorts, a standard 3+3 dose escalation has been implemented with two dose schedules in parallel, Q1W and Q3W. Objectives include evaluation of safety and tolerability, PK, PD and preliminary anticancer activity of ALPN-202. Disease assessments are evaluated by RECIST v1.1 for solid tumors or by Lugano Classification for lymphoma. Results: As of January 2021, 20 subjects with advanced malignancies have received ALPN-202. Dose-dependent PK and target saturation have been preliminarily observed. So far, ALPN-202 has been well tolerated at dose levels ranging from 0.001 to 1 mg/kg weekly, with no DLTs. Low-grade skin toxicities (grade 1-2 rash) have been observed in 4 subjects (20%). Among 11 evaluable subjects, an unconfirmed partial response has been observed in one subject with colorectal carcinoma, while stable disease has been observed in 5 subjects with colorectal carcinoma, mesothelioma (2), cholangiocarcinoma, and renal cell carcinoma -- for a preliminary clinical benefit (PR+SD) rate of 100% (4/4) at dose levels of 0.3 mg/kg and higher, or 54% (5/11) overall (table). The meeting presentation will update this data, which is expected to include the conclusion of Q1W dose escalation, as well as immune correlates. Conclusions: First-in-human dose escalation with ALPN-202 has been well tolerated at doses capable of engaging CD28 costimulation in vivo in association with dual PD-L1/CTLA-4 checkpoint inhibition, with early signs of anti-tumor activity. These findings suggest that CD28 agonism can be safely achieved in humans, and further suggest that dose expansion with ALPN-202 is warranted to assess the relevance of controlled CD28 costimulation as a novel approach to cancer immunotherapy. Clinical trial information: NCT04186637. [Table: see text]

2579 Background: In preclinical studies, the combination of anti-VEGF/Ang2 and anti-PD-1 therapy has been shown to promote an immunopermissive state, which is supportive of T-cell-mediated tumor cell destruction. BI 836880 is a humanized bispecific nanobody that targets VEGF and Ang2, and ezabenlimab (BI 754091) is an anti-PD-1 antibody. Phase I studies investigating each as monotherapies have reported safety and preliminary antitumor activity. This ongoing Phase Ib study is evaluating the combination of BI 836880 and ezabenlimab in pts with advanced solid tumors. In Part 1 (dose escalation), the combination was feasible in pts with advanced NSCLC, with a recommended Phase II dose (RP2D) of BI 836880 720 mg + ezabenlimab 240 mg IV q3w. Here, we report updated results from Part 2 (expansion phase), which is assessing the antitumor activity and safety of the RP2D. Methods: Seven cohorts are currently recruiting pts in Part 2: metastatic (m) NSCLC after checkpoint inhibitor (CPI) monotherapy (Cohort A); mNSCLC after chemotherapy (CT) + CPI (Cohort B); mSCLC after CT ± CPI (Cohort C); 1st and 2nd recurrences of glioblastoma (GBM; Cohort D); immunotherapy-resistant m-melanoma (Cohort E); hepatocellular carcinoma (HCC) after prior sorafenib or lenvatinib ± CPI (Cohort F); and previously untreated/unresectable HCC (Cohort G). Primary endpoint is objective response rate (complete response + partial response [PR]). Results: As of January 2021, 196 pts have received BI 836880 plus ezabenlimab (14 in Part 1, 182 in Part 2 [Cohort A, 26; B, 30; C, 19; D, 31; E, 32; F, 28; G, 16]). 134 (68%) pts were male, median age was 63 years and 102 (52%) had prior CPI use. Any grade and ≥G3 adverse events (AEs; any cause) were reported by 160 (82%) and 62 (32%) pts, most commonly (all%/≥G3%) hypertension (20/8), asthenia (20/3), diarrhea, decreased appetite, and nausea (all 11/1). 95 (48%) pts had a drug-related AE, most commonly hypertension and asthenia (both 11%). 6 pts had a G4 AE (non-related: hyperkalemia + cardiac arrest, laryngospasm, gastrointestinal perforation; drug-related: anaphylactic reaction, acute pancreatitis, transaminases increased); 8 pts had a G5 AE (non-related: general physical health deterioration, epilepsy, hemoptysis, cardio-respiratory arrest, hepatic failure, intracranial hemorrhage, COVID-19 pneumonia; drug-related tracheal hemorrhage). 30 (15%) pts had immune-related AEs (3% ≥G3), including hypothyroidism (3%). 11 (6%) pts had an AE leading to discontinuation. Overall, 145 pts were evaluable for response: 9 pts achieved confirmed PR (2 pts in Part 1 and 7 in Part 2 [NSCLC, n = 3; SCLC, n = 1; GBM, n = 1; melanoma, n = 1; and 2nd-line HCC, n = 1]), 87 pts had stable disease and 49 pts had progressive disease. 111 pts remain on treatment. Conclusions: BI 836880 plus ezabenlimab had a manageable safety profile. The combination showed preliminary antitumor activity in a range of tumor types. Clinical trial information: NCT03468426.

e15125 Background: APL-501 is a humanized monoclonal antibody targeting programmed cell death-1 (PD-1). APL-501 is being evaluated in patients (pts) with advanced recurrent and relapsed solid tumors who had not been previously treated with an immune checkpoint inhibitor in an ongoing 3-part Phase 1 trial (NCT03053466). Herein, we present the emerging pharmacokinetic (PK) and receptor occupancy (RO), safety and preliminary efficacy. Methods: Weight-based dose escalation (1, 3, and 10 mg/kg, Part 1) and Extension (Part 2) has been completed and the study is currently enrolling specific tumor types (MSI-H/dMMR and Carcinoma of Unknown Primary [CUP]) into the Expansion Cohorts (Part 3). Relapsed/refractory solid tumor pts were enrolled in Part 1 and Part 2. Key exclusion criteria included prior therapy targeting PD-1/PD-L1 and uncontrolled CNS metastases. APL-501 was administered IV over 1 hour every 14 days. Serum and PBMCs were collected for PK and RO analysis, respectively. RO was assessed using different T-cell markers measured by flow cytometry of PBMC. Anti-tumor activity was assessed by investigators using RECIST and irRECIST. Safety was assessed using CTCAE, v4.03. Results: As of 31 Dec 2019, 22 pts were enrolled with a mean age of 62.1 (SD: 12.2) years. ECOG PS 0/1 reported at 10/12 pts, respectively. Pts had a median number of 3 prior lines of therapy (range, 1 – 9) and median time to treatment from initial diagnosis was 30.1 months (range, 6.7 – 184.8). Across doses evaluated, APL-501 demonstrated dose proportional PK. One hundred percent (100%) RO was observed across all doses evaluated. No dose limiting toxicities were reported. Fifteen pts (68.2%) had related AEs; two pts (9.1%) had Grade ≥ 3 related AEs to APL-501. Eight pts had stable disease and two pts had partial response by RECIST (esophageal adenocarcinoma and CUP). Seven pts remained on therapy for ≥ 24 weeks. The recommended phase 2 dose (RP2D) has been determined to be 400 mg IV every 14 days (non-weight-based) based on safety and PK modeling. Conclusions: Preliminary results indicate clinical activity of APL-501 in relapsed/refractory malignant disease with a generally tolerable safety profile. The PK and RO profile, across all doses evaluated, appears comparable to marketed PD-1 inhibitors. Continued exploration of APL-501 with the RP2D in CUP and MSI-H/dMMR tumors is being planned. Clinical trial information: NCT03053466 .

9557 Background: There is growing evidence to suggest synergism between stereotactic ablative radiotherapy (SABR) and immunotherapy (IO) against metastatic melanoma. The optimal timing and dosing of SABR for this purpose has not been established. Here, we report results from a Phase I trial, finding the best outcomes with low dose SABR delivered late. Methods: Metastatic melanoma pts with at least two metastases received SABR to a single metastatic site. All pts had standard dose IO with anti-PD1 and/or anti-CTLA4. Following a standard 3+3 design, pts were escalated through three SABR doses (10Gy, 15Gy and 20Gy) delivered at three different time points (Cycle 1, 2, or 3 of IO). Dose limiting toxicity (DLT) were defined as Grade 3 or higher toxicity within 3 months of first treatment and assessed by an independent data safety monitoring committee (IDSMC). Logistic or cox regressions were used to assess the impact of SABR dose, timing and use of combination IO on toxicity, progression-free (PFS) and overall survival (OS) while controlling age, gender and baseline performance status. Results: Between April 2016 and August 2018, 24 pts were enrolled. The median age was 66 years and most were ECOG 0-1 (92%). The median follow-up was 10 months. Three pts (12.5%) developed DLTs (enterocolitis, hepatitis and liver function derangement). None occurred at SABR treated sites and all were in pts receiving 15Gy. DLTs were not associated with SABR timing (p = 0.44) or use of combination IO (p = 0.72). On this basis the IDSMC recommended stopping the trial and maximum tolerated SABR dose was defined at 10 Gy. The median PFS and OS were respectively 5.4m (95% CI 2.1m-NR) and 16.9m (95% CI 7.1m-NR). The median PFS for those receiving 10Gy was numerically higher than those receiving 15Gy (11.8m vs 2.6 m, p = 0.42). The only treatment related factor associated with improved PFS (HR = 0.14, p = 0.02) and OS (HR = 0.09, p = 0.04) was receiving SABR with Cycle 3. SABR dose (PFS p = 0.75, OS p = 0.67) and IO type (PFS p = 0.13, OS p = 0.06) were not significant. Conclusions: SABR combined with IO is generally safe overall. We found the optimal therapeutic index may be achieved with 10Gy delivered with the third cycle of IO; a strategy that warrants further testing. Clinical trial information: ACTRN12616001064493.

3059 Background: Poly (ADP-ribose) polymerase (PARP) enzymes play critical roles in DNA damage detection and repair. IMP4297 is a novel, potent PARP1/2 inhibitor (IC50 6.27nM/1.57nM) and has demonstrated to be 20-fold more potent than Olaparib in anticancer animal models. Two phase I studies were performed to evaluate and characterize the tolerability and safety, pharmacokinetics, and antitumor activity of single agent IMP4297 in Chinese and Australian patients with advanced ovarian, breast, prostate and other solid tumors. Methods: Dose escalation used a 3+3 design with a modified Fibonacci escalation. Dose cohort expansion was planned after efficacy was observed at the lowest dose level. Patients received IMP4297 monotherapy orally once a day until disease progression or unacceptable toxicity. Results: As of Jan 12, 2019, 56 patients, including 23 BRCA mutation carriers (BRCA+), had been enrolled at 2-100 mg dose level. No DLT was observed. In these two studies, the most frequent treatment-related adverse events (TRAEs) were leukopenia (20%), followed by anemia (18%), nausea (18%) and thrombocytopenia (14%). The majority of TRAEs were grade 1 or 2. Grade 3 TRAEs occurred in five patients (anemia, n=2; vomiting, n=1; thrombocytopenia, n=1; elevated AST, n=1). Only one patient had a dose reduction due to grade 3 thrombocytopenia. No serious TRAEs were observed. In 15 BRCA+ patients who had measurable lesions, the ORR was 33% and the DCR was 80%. There were 4 BRCA+, platinum-sensitive ovarian cancer patients with an ORR of 75% and a DCR of 100%. One patient with somatic BRCA mutated urothelial carcinoma showed a 76% decrease in tumor size. Conclusions: IMP4297 has been well-tolerated with significant anti-tumor activity. The 100 mg daily dose was selected as the RP2D based on safety, pharmacokinetics and clinical activity, and will be further characterized in dose expansion and phase II studies. Tumor response to treatment (RECIST 1.1) in patients with measurable lesions. Clinical trial information: NCT03508011 and NCT03507543. [Table: see text]

3029Background: MK-1248 is a humanized IgG4 agonist monoclonal antibody (mAb) that targets GITR. GITR is expressed on regulatory T cells (Treg), resting CD4+ and CD8+ T cells, NK (natural killer) c...

TPS3113Background: Programmed cell death-1 (PD-1) and its ligand, programmed death-ligand 1 (PD-L1), play critical roles in the immune modulation of tumor progression. Tislelizumab is a humanized I...

445 Background: Monoclonal antibodies (mAb) against programmed cell death-1 (PD-1) have demonstrated antitumor activity across multiple malignancies. BGB-A317 is a humanized IgG4 mAb with high affinity and binding specificity for PD-1. Previous reports from an ongoing Phase 1A/1B study (NCT02407990) in patients with advanced solid tumors suggested that BGB-A317 was generally well tolerated and had antitumor activity in multiple tumor types. Here, we present the preliminary results from a subset of patients with UC enrolled in this study. Methods: Patients with UC received intravenous BGB-A317 at doses of 2, 5, 10 mg/kg Q2W or Q3W and 200 mg Q3W. Tumor cell (TC) and immune cell (IC) PD-L1 expression was retrospectively assessed with the VENTANA PD-L1 (SP263) assay. Safety and tolerability was assessed by monitoring adverse events (AEs) and antitumor effects were assessed by RECIST v1.1 criteria. Results: As of 8 June 2017, 15 patients with UC (median age, 72 yr [range: 39–79]) received BGB-A317 during phases 1A (n = 8) and 1B (n = 7). All patients were Caucasian and 13 patients were male; the median number of prior systemic anticancer therapies was 1 (range: 0–4). Median duration of treatment was 115 d (range: 27–476); 6 patients remain on treatment. The most common treatment-related AEs (TRAEs) were fatigue (n = 5) and rash (n = 3); grade ≥3 TRAEs included fatigue (n = 1), and hyperglycemia and type 1 diabetes mellitus (T1DM; n = 1). Serious TRAEs occurred in 2 patients (infusion-related reaction [n = 1]; hyperglycemia and T1DM [n = 1]). All patients were evaluable for response assessment. Confirmed complete and partial responses occurred in 1 and 3 patients, respectively, for a response rate of 27%; the disease control rate (CR+PR+SD) was 53%. Nine samples were available for PD-L1 evaluation. Responses were observed in 3 of 6 patients with PD-L1+ tumors (defined as ≥25% TC or IC expressing PD-L1 by IHC) while 1 in 3 patients with PD-L1– tumors responded. Conclusions: BGB-A317 was generally well tolerated in patients with UC and objective responses were observed in both PD-L1+ and PD-L1– diseases. BGB-A317 is currently being investigated in China as monotherapy for patients with PD-L1+ UC (CTR20170071). Clinical trial information: NCT02407990.

645 Background: Activating V600 BRAF mutations are detectable in around 10% of mCRC pts and are associated with poor prognosis. Low response rates have been reported with anti-BRAF monotherapy in this subset of pts while encouraging data exist on enhanced MAPK pathway inhibition with combination therapy (anti-BRAF + anti-MEK and/or anti-EGFR). Methods: We performed a pooled analysis of BRAF-mut mCRC pts enrolled into different phase 1 trials involving the use of anti-BRAF monotherapy alone (Group A) or in combination with a MEK inhibitor (Group B) at therapeutic doses between June 2012 and August 2016. Demographic, baseline, toxicity and efficacy data were retrospectively reviewed. Results: Twenty BRAF-mut mCRC pts were identified in either Group A (n = 13) or Group B (n = 7). All pts had an ECOG performance status ≤ 1. Median age was 54 years (range 33-74). The primary tumor was right-sided in 10 (50%) pts, left-sided in 9 (45%) pts, and unknown in 1 (5%) subject. Median number of previous treatment lines was 1 (range 1-4). The disease control rate was 55%, with 3 (15%) pts experiencing partial response (PR) and 8 (40%) with stable disease. No complete responses were observed, 8 (40%) pts had progressive disease and 1 subject was considered not evaluable. All PRs were achieved in Group B and had duration of 2-4 months (mo). Median PFS was 3.73 mo (95% confidence interval [CI] 3.06-6.79) in the overall population, and showed a trend favoring the combination arm (2.80 mo for Group A vs. 5.03 mo for Group B, hazard ratio 0.71 [CI 0.26-1.95], p = 0.503). Most common toxicities were skin-related side effects (n = 10; 50%), myalgia/arthralgia (n = 5; 25%), nausea (n = 3; 15%), and pyrexia (n = 3; 15%). Grade 3/4 toxicities were uncommon and manageable: neutropenia (n = 1; 5%), hypophosphatemia (n = 1; 5%), pyrexia (n = 1; 5%), and abdominal pain (n = 1; 5%). Conclusions: Our cohort of pts treated with BRAF +/- MEK inhibitors showed a favorable safety profile. An encouraging activity level was found in the combination arm. In line with existing literature data, our findings supporting further development of combined MAPK inhibition in V600-positive mCRC.

e14513Background: A high neutrophil/lymphocyte ratio (NLR) at baseline has repeatedly been associated with shorter progression free (PFS) and overall survival (OS). We explored whether early change...

8063 Background: Both intrinsic and acquired resistance mechanisms to ALK inhibitors have been observed in ALK rearranged (ALK+) non-small cell lung cancer (NSCLC). TSR-011 inhibits ALK (IC50 = 0.7...