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4532 Background: Standard first-line regimens for patients with metastatic gastroesophageal adenocarcinomas have moderate clinical benefit with objective response rates (ORR) of approximately 40-50%. FOLFIRINOX has been shown to be an effective and well-tolerated first line therapy in other GI cancers. In this open-label, single-arm phase II study of patients with advanced gastroesophageal adenocarcinomas, we sought to evaluate the safety and clinical activity of FOLFIRINOX. Methods: The primary endpoint was ORR, and secondary endpoints included safety profile, progression free survival (PFS), overall survival (OS), time to progression (TTP), clinical benefit rate (CBR), and duration of response. Estimated sample size included 41 patients with HER2 negative disease with 90% power to detect an ORR≥60% with alpha of 0.10. No enrollment goal was planned for HER2 positive patients, but they were allowed participation to receive study treatment in combination with trastuzumab. Treatment consisted of 400mg/m2 5-FU bolus, 400 mg/m2 leucovorin, 2400 mg/m2 5-FU infusion over 46 hours, 180 mg/m2 irinotecan, and 85 mg/m2 oxaliplatin. Trastuzumab was administered intravenously as a 6 mg/kg loading dose then given 4 mg/kg every 14 days for HER2 positive patients. This trial is registered with ClinicalTrials.gov, NCT01928290. Results: From November 2013 to May 2019, 67 patients were enrolled, of which 26 (39%) had HER2 positive disease. Median follow-up was 16.1 months. ORR was 61% (25/41) for HER2 negative and 85% (22/26) for HER2 positive groups. Overall, one patient (2%) had a complete response, 36 patients (69%) had partial responses, and 13 patients (19%) had stable disease for >6 months; therefore, CBR was 96%. Median PFS was 11.9 months, median OS was 17.4 months. 41 patients (83.7%) had dose modification or treatment delay with the most common toxicities being neutropenia, diarrhea, peripheral sensory neuropathy, and nausea with no unexpected toxicities. Conclusions: FOLFIRINOX is a highly effective three-drug regimen for first-line treatment of advanced gastroesophageal cancer with expected, tolerable toxicities. Clinical trial information: NCT01928290 .

89 Background: Standard first-line regimens for patients with metastatic gastroesophageal adenocarcinomas have an approximate 40% objective response rate (ORR). FOLFIRINOX has been used in first line therapy in other GI cancers (i.e pancreatic and CRC) with impressive efficacy signals. Methods: This is a phase II study of first line combination chemotherapy with fluorouracil (5-FU), irinotecan, and oxaliplatin in patients with advanced gastric, esophageal, or gastroesophageal junction adenocarcinoma (NCT01928290). Starting doses were 5-FU 400mg/m2 bolus followed by 2400 mg/m2 over 46 hours with leucovorin 400 mg/m2, irinotecan 180 mg/m2, and oxaliplatin 85 mg/m2. Trastuzumab was administered as 6 mg/kg loading dose then 4 mg/kg every 14 days if patients had HER2+ cancer. The primary endpoint was overall response rate (ORR). Secondary endpoints included progression free survival (PFS), overall survival (OS), time to progression (TTP), clinical benefit rate (CBR), and duration of response. Enrollment of 41 patients with HER2- disease was planned to reach one-sided = 0.10 and power 0.90 with goal of detecting true ORR60%. No enrollment goal was planned for HER2+. Results: From Nov 2013 to July 2017, 58 patients were enrolled, 25 out of 58 (43%) had HER2+ disease. Forty-nine patients were evaluable for response as they completed at least one restaging scan. ORR was 78% (38/49) in all patients, 67% (18/27) in HER2-, 91% (20/22) in HER2+. One patient (2%) had complete response, 37 (76%) had partial response, 7 (14%) had stable disease > 6 months; therefore, CBR was 92%. Median PFS is 11.9 months, median OS is 17.4 months and median follow up time 16.1 months. 41 (83.7%) had dose modification or delay during treatment. There were no unexpected toxicities. Conclusions: FOLFIRINOX with or without trastuzumab showed remarkable ORR and PFS in patients with advanced gastroesophageal adenocarcinoma in the first-line setting. This regimen may be a reasonable therapeutic option for patients with preserved performance status. Further investigation in larger population is warranted. Clinical trial information: NCT01928290.

553 Background: Preoperative radiotherapy (RT) with 5FU chemotherapy (CT) is a standard of care for cT3-4 rectal cancer. Studies incorporating additional cytotoxic agents have resulted in increased morbidity with little benefit. We evaluate a template that seeks to (1) include the known benefits of preoperative RT on local response/control, (2) provide for preoperative multi-drug CT, (3) avoid the morbidity of concurrent RT and multi-drug CT. Methods: Patients with cT3-4, any N, any M rectal cancer were eligible. Patients were confirmed to be candidates for surgery, provided the response was sufficient. Preoperative treatment was 5 fractions RT (25 Gy to involved mesorectum, 20 Gy to elective nodes), followed by 4 cycles of mFOLFOX6. Postoperative CT was at the discretion of the medical oncologist. The principal objectives are to demonstrate that this regimen can achieve T stage down staging (ypT < cT) and acute grade 3+ gastrointestinal (GI) morbidity equal to or better than historical controls. Results: Accrual opened late 2009, with 60 patients enrolled through 8/2011. Forty-six have had sufficient time to proceed to surgery with 4 having grade 3 preoperative GI morbidity. Two cases are inevaluable for response: one withdrew consent prior to CT and one received no surgery due to progression of cM1 disease (with local response). The 44 evaluable cases included 4 cT4 and 40 cT3; 32 (73%) cN+, 4 cM1. At surgery 33 (75%) had ypT0-2 residual disease including 13 (30%) ypT0, 14 (32%) were ypN+. Cases were sub-analyzed by whether disease was too advanced for the upcoming ACOSOG preoperative FOLFOX vs. 5FU-RT trial. By ACOSOG eligibility, response rates were (eligible first, ineligible second) ypT0: 10/22 (45%) vs. 3/22 (14%) (p = 0.05), ypT0-2: 19/22 (86%) vs. 14/22 (64%) (p = NS). Conclusions: This regimen achieves high response rates with acceptable morbidity. The response for ACOSOG eligible cases meets pre-determined stopping criteria for proceeding to a randomized trial. Our successor study will randomize to this regimen vs. FOLFOX alone for ACOSOG eligible cases, while initially continuing as a single arm trial for ACOSOG ineligible cases.