The influence of treatment response on the impact of resection margin status after preoperative chemoradiotherapy in rectal cancer.

Abstract

505 Background: Circumferential resection margin (CRM) and distal resection margin (DRM) have different impact on clinical outcomes after preoperative chemoradiotherapy (CRT) followed by surgery. Effect and adequate length of resection margin as well as impact of treatment response after preoperative CRT was evaluated. Methods: Total of 403 patients with locally advanced rectal cancer underwent preoperative CRT followed by total mesorectal excision between January 2004 and December 2010. After applying the criterion of margin less than 0.5 cm for CRM and/or less than 1 cm for DRM, 158 cases were included as a study cohort. All patients underwent conventionally fractionated radiation with dose over 50 Gy and concurrent chemotherapy with 5-FU or capecitabine. Median follow-up duration was 44.9 months. Results: The 5-year overall survival (OS), disease-free survival (DFS), locoregional relapse-free survival (LRFS), and distant metastasis-free survival (DMFS) were 83.3%, 75.6%, 86.3%, and 77.4% respectively. CRM of 1.5 mm and DRM of 7 mm were cutting points showing maximal difference using maximal chi-square method. In univariate analysis, the shorter CRM was significantly related with worse clinical outcomes, whereas DRM was not. In multivariate analysis, CRM of 1.5mm, ypN, and perineural invasion were prognosticators for OS, DFS, LRFS, and DMFS. CRM was not a significant prognostic factor for good responders, defined as patients with near total regression or T down-staging. However, poor responders demonstrated a significant difference according to the CRM status. Conclusions: Close CRM, defined as 1.5 mm, was a significant prognosticator, but the impact was different for treatment response. Postoperative treatment strategy may be individualized based on this finding. However, findings from this study needs to be validated with larger independent cohort. [Table: see text]