Adjuvant treatment for resected rectal cancer: impact of standard and intensified postoperative chemotherapy on disease-free survival in patients undergoing preoperative chemoradiation-a propensity score-matched analysis of an observational database

Adjuvant chemotherapy for resected rectal cancer is widely used. However, studies on adjuvant treatment following neoadjuvant chemoradiotherapy (CRT) and total mesorectal excision (TME) have yielded conflicting results. Recent studies have focused on adding oxaliplatin to both preoperative and postoperative therapy, making it difficult to assess the impact of adjuvant oxaliplatin alone. This study was aimed at determining the impact of (i) any adjuvant treatment and (ii) oxaliplatin-containing adjuvant treatment on disease-free survival in CRT-pretreated, R0-resected rectal cancer patients. Patients undergoing R0 TME following 5-fluorouracil (5FU)-only-based CRT between January 1, 2008, and December 31, 2010, were selected from a nationwide registry. After propensity score matching (PSM), comparison of disease-free survival (DFS) using Kaplan-Meier analysis and log-rank test was performed in (i) patients receiving no vs. any adjuvant treatment and (ii) patients treated with adjuvant 5FU/capecitabine without vs. with oxaliplatin. Out of 1497 patients, 520 matched pairs were generated for analysis of no vs. any adjuvant treatment. Mean DFS was significantly prolonged with adjuvant treatment (81.8 +/- 2.06 vs. 70.1 +/- 3.02 months, p < 0.001). One hundred forty-eight matched pairs were available for analysis of adjuvant therapy with or without oxaliplatin, showing no improvement in DFS in patients receiving oxaliplatin (76.9 +/- 4.12 vs. 79.3 +/- 4.44 months, p = 0.254). Local recurrence rate was not significantly different between groups in either analysis. In this cohort of rectal cancer patients treated with neoadjuvant CRT and TME surgery under routine conditions, adjuvant chemotherapy significantly improved DFS. No benefit was observed for the addition of oxaliplatin to adjuvant chemotherapy in this setting.