Comparative analysis of adjuvant chemoradiotherapy vs. tegafur/gimeracil/oteracil monotherapy vs. observation alone in gastric cancer patients after gastrectomy plus D2 lymph node dissection: A single-center 15-year retrospective study.

e16096 Background: The surgical management of gastric cancer in lymph nodes dissection (LND) differ between Eastern and Western countries. Western countries typically practice D0 to D1 LND followed by postoperative chemoradiotherapy (CCRT). In contrast, East Asian countries treat extensive D2 LND as the standard, followed by adjuvant chemotherapy, which confers to 5-10% relapse-free and overall survival benefit in the long-term. It remains unclear whether chemoradiotherapy was superior adjuvant chemotherapy in gastric cancer patients who received gastrectomy plus D2 LND. Previous studies had led to inconsistent result. Regarding the comparison of adjuvant CCRT versus gastrectomy plus D2 LND alone, retrospective studies may not be conclusive and are limited by unadjusted selection biases. From August 2008 to December 2023, our institution treated 600 patients with gastric cancer who underwent gastrectomy with D2 LND. We identified and categorized 348 patients into adjuvant CCRT (etoposide/leucovorin/fluorouracil, ELF) group, adjuvant chemotherapy (tegafur/gimeracil/oteracil, TS-1) group, and surgery alone group. We aims to compare the overall survival (OS), relapse-free survival (RFS), and pattern of failure (POF) between the treatment groups in a single institution. Methods: We analyze the impacts of three modalities on survival outcome by Cox proportional hazard model. The variables include type of adjuvant treatment, age, sex, BMI, pathological stage, degree of differentiation, involved lymph node ratio, stomach site, and type of surgery. As a comparison, we perform propensity score matching (PSM) and calculate the hazard ratio for either two of three groups and have another three cohorts, which are chemo-radiotherapy vs. Observation, Chemo-radiotherapy vs. TS-1, and TS-1 vs. Observation. Results: Both CCRT with ELF regimen and TS-1 offers RFS and OS benefits in locally advanced gastric patients after gastrectomy plus D2 LND as compared to observation alone. TS-1 monotherapy has a trend better than CCRT in terms of RFS and OS. Local and regional relapse are not significantly decreased in CCRT group as compared to TS-1 group. Conclusions: CCRT with ELF regimen confers RFS and OS benefit in locally advanced gastric cancer patient after gastrectomy plus D2 LND. CCRT is not superior to TS-1 in terms of survival outcome or loco-regional control. Failure pattern after each adjuvant modality. Local Regional Distant Total Adjuvant_Tx Surgery alone 4 (3.3%) 18 (14.8%) 22 (18.0%) 122 CCRT 8 (6.3%) 40 (31.3%) 24 (18.8%) 128 TS-1 9 (9.2%) 20 (20.4%) 13 (13.3%) 98 P value 0.1865 0.0064 0.5114 348 CCRT is not superior to TS-1 or surgery alone in terms of local or regional control.