Combined modality for localized gastric diffuse large B-cell lymphoma: Long-term outcomes of 50 patients.

7079 Background: R-CHOP is the primary treatment for gastric diffuse large B-cell lymphoma (GDLBCL); for localized disease, the role of consolidative radiation therapy (RT) after chemotherapy remains underexplored. This study focuses on localized GDLBCL undergoing a combined modality therapy of R-CHOP followed by gastric RT, comparing outcomes between those receiving short-course (3-4 cycles) and full-course (6 cycles) R-CHOP. Methods: A retrospective analysis identified 50 consecutive PGDLBCL pts treated with R-CHOP followed by RT between 1/2000-1/2021. Baseline characteristics and follow-up data were collected. Lugano PET criteria and endoscopy (EGD) assessed overall response rate. Kaplan-Meier and univariable cox regression models estimated overall survival (OS) and (PFS). Results: Of the 50 pts with localized (Stage I-II) disease, 34 (68%) received 3-4 cycles of R-CHOP and 16 (32%) received 6 cycles. Pre-RT disease evaluation varied, with 36 (72%) undergoing EGD and PET, 4 (8%) EGD and CT, and 6 (12%) PET alone. One pt (3%) exhibited active DLBCL post 3-4 cycle R-CHOP, while 5 (31%) did so after 6 cycles (p=0.1). Median time from last R-CHOP dose to RT start date was 1.2 months with a median 3060 cGy delivered dose for both groups (range 2340-3060 in the 3-4 cycle group, 3000-4500 in the 6-cycle group). Median follow-up time from RT end is 58 months. No in-field failures occurred post-complete response (CR); however, 1 pt did not achieve a CR following R-CHOP and RT, progressing in the stomach and subsequently at new, out-of-field (OOF) sites. 3 pts had OOF progression without relapses in the stomach in a median time of 21 months. Low-grade lymphoma in the stomach post-DLBCL CR was observed in 2 pts, 3 and 22 months from RT end, with 1 OOF marginal zone lymphoma 2 years-post RT. OS and PFS did not significantly differ between the 3-4 and 6 cycle groups (96-month OS 70% vs. 86%, p=0.8; 96-month PFS 76% vs. 86%, p=0.7). OS and DLBCL PFS were analyzed for pts with evidence of residual DLBCL pre-RT compared to those without evidence of disease after R-CHOP. The 24-month DLBCL PFS was 92% in the CR group and 67% for those with incomplete response (p=0.14), with 92% and 67% 24-month survival probability (p=0.11). On univariate analysis, pre-RT evidence of active DLBCL by PET and/or EGD, pre-RT PET FDG uptake, and achieving CR on first-post-RT imaging were not statistically significant for DLBCL PFS. Conclusions: Recognizing the limitations of a retrospective study, our study documents the effectiveness of short-course R-CHOP followed by RT in localized GDLBCL, with similar outcomes to the full 6-cycle regimen. Excellent disease control was observed, with few instances of DLBCL or low-grade lymphoma relapse. Further analysis will include a cohort receiving R-CHOP alone without consolidative RT. This analysis aims to contribute to the evolving standard of care for GDLBCL, providing insights for future treatment strategies.