583PIMPACT OF ADJUVANT CHEMOTHERAPY (AC) ON RELAPSE-FREE SURVIVAL (RFS) IS DIFFERENT ACCORDING TO POST-CHEMORADIATION PATHOLOGIC STAGE (YPSTAGE) IN RECTAL CANCER.

ABSTRACT Aim: In contrast with colon cancer, survival benefit from adjuvant chemotherapy (AC) in rectal cancer is still unclear. For patients (pts) who are treated with preoperative chemoradiation (preop CRT), post-chemoradiation pathologic stage (ypStage) is known to be a major determinant of long term outcome. We aimed to describe clinical benefit from AC in terms of relapse-free survival (RFS) according to ypStage in rectal cancer. Methods: Retrospective analysis was done for data which were derived from prospective database of preop CRT - treated pts in National Cancer Center, Korea. Pts with initially nonmetastatic rectal cancer who received preop CRT followed by surgery (Jan 2001–Dec 2009) were included. Completeness of AC schedule was reviewed: undergoing chemotherapy cycles covering at least 16 weeks was considered completion. Results: Among a total of 743 pts, ypT0N0 or ypTisN0 (ypStage 0) / ypStage I/ ypStage II/ ypStage III/ ypStage IV were 119 (16.0%), 192 (25.9%), 203 (27.3%), 219 (29.5%), 10 (1.4%), respectively. 625 (84.1%) completed scheduled AC (fluoropyrimidine monotherapy in 95%), and 88 (11.8%) omitted or stopped AC, while 30 (4.0%) were excluded due to follow-up loss or disease progression. Completing AC was not associated with RFS in all pts (5-yr RFS 75.9% vs 73.6%, hazard ratio for relapse (HR) 0.95, p = 0.84), but significantly affected RFS in ypStage III (5-yr RFS 56.6% vs 21.4%, HR 0.45, p = 0.014). Among ypStage 0, I, and II, completing AC was not related to RFS (5-yr RFS 85.0% v 84.1%, HR 1.01, p = 0.969). Multivariate analysis revealed completion of AC was still a significant predictor of RFS after adjustment to initial carcinogembryonic antigen (CEA) level, nodal stage, and circumferential margin (CRM) status (table). HR (95% confidence interval) p value initial CEA 1.83 (1.22 - 2.76) 0.004 ypN2 2.08 (1.38 - 3.16) 0.001 completion of AC 0.37 (0.20 - 0.70) 0.002 positive CRM 2.21 (1.18 - 4.15) 0.014 Conclusions: Completion of AC affected RFS in ypstage III rectal cancer, while it did not in earlier stages. This study suggests survival benefit from AC could be limited to ypStage III in preop CRT treated rectal cancer. Disclosure: All authors have declared no conflicts of interest.