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709 Background: Pancreatic ductal adenocarcinoma (PDAC) has a poor prognosis, with a 5-year survival rate of 10%. The current standard of care for patients with resectable disease is surgical resection followed by 6 months of adjuvant mFOLFIRINOX (mFFX) chemotherapy. As survival outcomes and distant recurrence rates improve with the use of mFFX, locoregional recurrence remains a significant cause of morbidity and mortality. We sought to integrate short-course proton radiation therapy (PRT) to the operative bed between cycles of adjuvant chemotherapy in patients with resected PDAC of the pancreatic head. Methods: Between 2019 and 2022, patients with resected PDAC with an R0 or R1 resection on adjuvant mFFX were enrolled in a phase I trial using a 3+3 dose-escalation schema (NCT03885284). Patients received mFFX as used in the PRODIGE 24 study and also received short-course PRT delivered over 1 week in 5 fractions (5 GyE each) between cycles 6 and 7 of mFFX. In dose level 1 (DL1), patients received PRT on days 15-19 in a 28-day cycle before starting cycle 7, and in dose level 2 (DL2) patients received PRT on days 8-12 in a 21-day cycle before starting cycle 7. Results: Nine patients were enrolled on the trial, median age 66 (range 52-78). Five had R0 resections, 4 had R1 resections, and 5 had node-positive disease. No patients received preoperative therapy, and none underwent vein reconstruction. Three patients were enrolled on DL1 and 6 patients on DL2. One dose limiting toxicity (DLT) occurred at DL2 (prolonged grade 3 neutropenia resulting in discontinuation of mFFX after cycle 7). No other DLTs were observed. Four patients completed the planned 12 cycles of mFFX (range 7-12, median 11). None of the patients have had local recurrence. Five of 9 patients had recurrence: 3 in the liver, 1 in the peritoneum, and 1 in the bone. Six patients are still alive, 4 of whom are recurrence free. With a median follow up from date of chemotherapy start of 12.5 months, median time to disease recurrence was 12 months (95% confidence interval [CI] 4-not reached [NR]), and median overall survival has not been reached (95% CI 6-NR, 2-year survival rate 57%). Conclusions: PRT integrated within adjuvant mFFX was well-tolerated and no local recurrence was observed for patients with resected PDAC. These findings warrant being confirmed in a phase II trial. Clinical trial information: NCT03885284 .

371 Background: Insurance status predicts access to medical care in the United States. Previous studies show uninsured and government insured patients have worse outcomes than those with private insurance. However, the impact of insurance status on survival in patients with Gastrointestinal Neuroendocrine Tumors (GI-NETs) is unclear. We evaluate the association between insurance status and survival in patients with GI-NETs. Methods: Our analysis includes 2022 patients who had surgical resection of GI-NETs at 8 institutions in the U.S. Neuroendocrine Study Group. Patients were categorized based on insurance as private (PI), government (GovI) or uninsured (UI). Factors associated with insurance status were assessed by uni- and multi-variate analysis. Primary endpoint was overall survival. Results: Patient demographics between the insurance categories were similar in ECOG performance status and tumor size at presentation. GovI patients had a higher median age than PI or UI (66 vs. 54 vs. 56 years respectively; p

TPS874 Background: Colorectal cancer (CRC) is one of the few cancers in which aggressive local approaches to treat systemic metastases have resulted in clinical benefit. Despite these approaches 70-80% of patients (pts) with resectable metastatic disease will recur. The one-year recurrence rate for this population is ~40-50%. Immunotherapeutics have yet to be studied in this setting. To sensitize microsatellite stable (MSS) CRCs to immune therapies adjunctive therapies are required. Gross tumor microenvironments suppress systemic anti-cancer immune responses. Stereotactic body radiation therapy (SBRT) is commonly utilized to treat liver metastatic CRC, using very high doses of focused radiation to ablate tumors. This causes localized inflammation, a potential increase in immunogenic intra-tumoral and intra-lymphatic antigen release, and a rapid influx of responding immune cells. We hypothesize that radiotherapy-induced tumor necrosis, and surgical removal of the remaining immunosuppressive gross disease will enhance the immunogenicity of CRC and potentiate the effectiveness of PD-1 blockade. Methods: This is a single arm phase 1b investigator-initiated study (NCT02837263) to evaluate the use of pem in combination with ablative radiotherapy for the treatment of oligometastatic CRC. This study examines the sequential use of SBRT, then pem followed by resection of all known sites of disease and 6 months of adjuvant pem. Pts with MSS CRC with resectable liver metastatic disease who have received prior FOLFOX are eligible. The primary endpoints are safety/tolerability and the rate of cancer recurrence at 1 year. Secondary endpoints include time to disease recurrence, disease free survival and overall survival. This study is currently enrolling with a planned total accrual of 15 patients. Correlative studies examine PD-L1 status, tumor infiltrating lymphocytes, evidence of an abscopal effect, versican proteolysis as a novel immune biomarker, and the ability of multiparametric fluorodeoxyglucose (FDG) PET MR and fluorothymidine (FLT) PET CT to detect immune infiltration. Clinical trial information: NCT02837263.

216 Background: Neutrophil, monocyte and lymphocyte counts are important biomarkers of the tumor-induced systemic inflammatory response. A lower monocyte-to-lymphocyte ratio (MLR) and neutrophil-to-lymphocyte ratio (NLR) is associated with a favorable prognosis for certain tumors. However, this association has not yet been demonstrated in resected pancreatic neuroendocrine tumors (PNETs). The aim of this study was to investigate the prognostic significance of MLR and NLR in patients with resectable PNETs with regards to overall survival (OS). Methods: Eligible patients undergoing surgery for PNETs between 2000 and 2016 were identified using a national multi-center cohort dataset. Their pre-operative neutrophil, monocyte and lymphocyte counts were imported and NLR and MLR were calculated. Receiver operating characteristic (ROC) curve analysis was used to determine the optimal cut offs for NLR and MLR. Univariate analyses were used to compare patient factors and tumor characteristics in different groups. The difference in OS between high and low groups was explored with the use of Kaplan Meier curves and compared using log-rank tests. Results: A total of 635 patients were analyzed. Univariate analysis revealed that higher lymphocyte, low monocyte and low neutrophil counts were associated with improved OS (P = 0.0002, 0.014 and 0.011 respectively). The mean NLR and MLR level was 4.11 ± 0.219 and 0.4295 ± 0.0196, respectively. Lower NLR ( < 4) and lower MLR ( < 0.25) were significantly associated with improved OS (p < 0.001 & p < 0.0001). Median survival was 141 months in the low NLR group (n = 474) and 119 months in the high NLR group (n = 161). The median survival in the high MLR group (n = 464) was 120 months and has not been reached in the low MLR group (n = 171). On multivariate analysis, low MLR was independent predictor of improved OS when controlling for age, race and comorbidities (p < 0.001). Conclusions: For resectable PNETs, low pre-operative NLR and MLR levels are significantly associated with improved survival. NLRs and MLRs may serve as valuable markers to stratify PNET patients for subsequent therapies and clinical trial enrollment.

e15261 Background: The combination of nab-paclitaxel (nab-P) and gemcitabine (G) is a standard of care for patients (pts) with metastatic pancreatic ductal adenocarcinoma (PDA). This regimen was shown to improve PFS and OS for pts with PDA and was well-tolerated in the first-line setting. Limited data are available describing the use of this regimen in a general population and in the second-line setting. Methods: A single-institution retrospective chart review of pts who received the combination of nab-P and G for PDA from 2011-2014 was performed after Institutional Review Board approval. Results: A total of 27 pts were treated with this regimen. The median age was 59 years old (33-81) and the ECOG PS was 0 (22%), 1 (74%), and 2 (4%). 9/27 pts were treated in the first-line setting and a PFS of 5.5 months (mos) and an OS of 7.6 mos was observed. The benefit from nab-P and G in the second-line setting depended on the prior therapy. Nab-P and G were given following adjuvant G in 10 pts with a PFS of 2.3 mos...

131 Background: A recent randomized trial of peritoneal drain (PD) placement after pancreaticoduodenectomy concluded that placement of PDs decreased the frequency and severity of complications. The role of PD placement after total gastrectomy for gastric adenocarcinoma (GAC) is not well-established. Methods: Patients who underwent total gastrectomy for GAC at 7 institutions from the U.S. Gastric Cancer Collaborative from 2000-2012 were identified. Univariate and multivariate analyses were performed to evaluate the association of PD placement with postoperative outcomes. Results: 344 patients were identified and anastomotic leak rate was 9%.253 (74%) patients received a PD. Those with PD placed had similar ASA class, tumor size, TNM stage, and need for additional organ resection when compared to their counterparts with no PD. No difference was observed in the rate of any complication (54% vs. 48%;p=0.45), major complication (25% vs. 24%;p=0.90), or 30-day mortality (7% vs. 4%;p=0.51) between the two groups. In addition, no difference in anastomotic leak (9% vs. 10%;p=0.90), need for secondary drainage (10% vs. 9%;p=0.92), or reoperation (13% vs. 8%;p=0.28) was identified. On multivariate analysis, PD placement was not associated with a decrease in frequency or severity of postoperative complications. Subset analysis of patients stratified by whether they underwent concomitant pancreatectomy similarly demonstrated no association of PD placement with reduced complications or mortality. In patients who experienced an anastomotic leak (n=31), placement of PD was similarly not associated with a decrease in complications, need for secondary drainage, or mortality. Conclusions: Peritoneal drain placement after total gastrectomy for adenocarcinoma, regardless of concomitant pancreatectomy, is not associated with a decrease in the frequency and severity of adverse postoperative outcomes, including anastomotic leak and mortality, or decrease in the need for secondary drainage procedures or reoperation. Routine use of peritoneal drains is not warranted.

120 Background: A recent single institutional study demonstrated that jejunostomy feeding tubes (J-tubes) placed during resection of gastric adenocarcinoma (GAC) are associated with increased complications and no change in receipt of adjuvant therapy. Our aim was to validate these findings in a large multi-institutional cohort. Methods: All patients who underwent resection for GAC at 7 institutions participating in the U.S. Gastric Cancer Collaborative from 2000-2012 were identified. Patients with metastatic disease were excluded. Univariate and multivariate logistic regression were performed to assess the association of J-tubes with postoperative complications and receipt of adjuvant therapy. Subset analysis of patients who underwent total vs subtotal gastrectomy was also performed. Results: Of 965 patients, 837 were included for analysis, of whom 265 (32%) received a J-tube. Patients receiving J-tubes demonstrated greater incidence of preoperative weight loss, lower BMI, greater extent of resection, and more advanced TNM stage. J-tube placement was associated with increased infectious complications (36% vs 19%;p

115 Background: The optimal extent of lymphadenectomy in the treatment of gastric adenocarcinoma continues to be a subject of intense debate. We aimed to compare gastrectomy outcomes following limited (D1) or extended (D2) lymphadenectomy. Methods: Using the multi-institutional U.S. Gastric Cancer Collaborative database, we reviewed the morbidity, mortality, recurrence, and overall survival (OS) of 727 patients receiving D1 or D2 lymphadenectomies. Patients with stage IV disease, prior gastrectomy, and age 85 or greater were excluded. Multivariate analyses included variables with p values less than 0.1. Results: Between 2000 and 2014, 266 (36.6%) and 461 (63.4%) patients received a D1 and D2 lymphadenectomy, respectively. ASA class, mean number of comorbidities, grade, stage, and signet ring cell subtypes were similar between groups. Neoadjuvant and adjuvant chemotherapy was more common in the D2 group (p

118 Background: Linitis plastica (LP) describes a diffusively infiltrative gastric adenocarcinoma that portends poor prognosis. Current treatment guidelines do not differentiate between LP and non-LP cancers and it is not known if the same staging system should be applied to both situations. Methods: Using the multi-institutional U.S. Gastric Cancer Collaborative database, 869 patients with gastric adenocarcinoma who underwent resection between 2000-2012 were identified. Clinicopathologic, perioperative and survival outcomes of the 58 patients with LP were compared to the 811 patients without LP. Results: Advanced disease (stage III/IV) at presentation was more common in patients with LP compared to non-LP patients (90 vs 44%, p

100 Background: Whether perioperative blood transfusion has a negative prognostic effect on recurrence and survival in patients undergoing resection of gastric adenocarcinoma (GAC) is unknown. Methods: All patients who underwent resection for GAC from 2000-2012 at 7 institutions were identified. The effect of transfusion on recurrence-free (RFS) and overall survival (OS) in the context of adverse clinicopathologic variables was examined by univariate (UV) and multivariate (MV) regression analyses. Results: Out of 965 pts, 765 underwent curative intent, R0 resection. Median FU for survivors was 44 mos; 30-day deaths were excluded. Median estimated blood loss (EBL) was 250cc and 166 pts (22%) received perioperative RBC transfusions. 5-yr RFS was 51% in transfused and 61% in non-transfused patients (p=0.01). Median OS was decreased in patients receiving transfusions (19 vs 50 mos, p

338 Background: Retrospective data suggest that neoadjuvant therapy in patients with resectable pancreatic cancer may improve the R0 resection rate and potentially survival. We examined the impact of neoadjuvant therapy on survival rates at a population level for patients with resected pancreatic adenocarcinoma. Methods: Treatment and outcome data were obtained from the Surveillance, Epidemiology and End Results (SEER) Medicare database for patients with pancreatic adenocarcinoma, who underwent a curative intent pancreatectomy from 2001-2007. Patients were stratified by treatment (neoadjuvant vs no neoadjuvant therapy). Kaplan Meier curves were constructed to analyze survival. Cox proportional hazards regression models with and without propensity score weighting were performed to determine the effect of neoadjuvant therapy and race on mortality while adjusting for age, gender, race, marital status, SEER site, urban/rural location, income, education, year of diagnosis, and Charlson Comorbidity Score. Results: 2608 patients were included. 58.4% (n=1523) were between age 66-75 and 41.6% (n=1085) were age 76 or older. 94% (n=2459) did not receive neoadjuvant therapy and 6% (n=162) received neoadjuvant therapy. Patients undergoing neoadjuvant therapy were 28% less likely to experience death at one year (HR 0.72; 95% CI, 0.53-0.97; p=0.03). There was also a trend towards a lower risk of death in this group at 2 years (HR 0.82; 95% CI, 0.66-1.01; p=0.07). Conclusions: Patients with pancreatic adenocarcinoma who underwent neoadjuvant therapy followed by resection had an improved one-year survival relative to patients who did not receive neoadjuvant therapy in this cohort. This effect may partially reflect the role of neoadjuvant chemotherapy in allowing for better selection of patients likely to benefit from surgery. To our knowledge this is the first population-based study that suggests an improved survival in patients with pancreas cancer undergoing neoadjuvant therapy prior to resection. [Table: see text]