Role of adjuvant chemotherapy following chemoradiation and surgery for locoregionally advanced rectal cancer: A Veterans Health Administration analysis

741 Background: Adjuvant chemotherapy (AC) following chemoradiation (CRT) and total mesorectal excision (TME) for locoregionally advanced rectal cancer (LARC) is a standard of care in the United States despite limited data. The purpose of this study was to examine the role, optimal regimen, and duration of AC in the mandatory, prospectively collected cancer registry of the largest integrated health system in the US. Methods: Using the VA Central Cancer Registry, stage II-III rectal cancer patients diagnosed between 1/2001-4/2011 were included if they received neoadjuvant CRT followed by TME with or without AC. Adequate chemotherapy was defined as at least 4 months of therapy. Kaplan-Meier and Log-Rank tests were used to assess survival. Propensity score (PS) adjustment was performed to compare survival outcomes while adjusting for baseline characteristics, including AJCC stage, age, gender, race, smoking status, and comorbidity. Results: 649 patients were identified; 323 received AC while 326 did not (OBS). Median follow-up was 66 months. Mean age was 63 years. 85.1% were white; 98.8% were male. 49.2% had stage II disease. Median overall survival (OS) for all patients was 92 months; 6-year OS was 56.8%. Median OS was 72 months for the OBS group and not reached (NR) for the AC group (p < 0.001). OS at 6 years was 49.5% for OBS and 64.1% for AC (p < 0.0001). On PS matched analysis, OS was improved favoring AC (p < 0.0001). Median disease-specific survival (DSS) was NR for the whole group and NR for the OBS and AC groups. 6-year DSS was 73.6% for the whole group and 67.9% for OBS vs. 79.2% for AC (p < 0.001). PS matched analysis for DSS favored AC (p = 0.0004). There was no significant difference in OS (p = 0.554) or DSS (p = 0.680) when comparing single versus multi-agent chemotherapy and no significant difference in OS (p = 0.766) or DSS (p = 0.271) when comparing adequate ( > / = 4 months) versus inadequate chemotherapy ( < 4 months). Conclusions: In this VA population of LARC patients treated with neoadjuvant CRT followed by TME, the addition of AC was found to improve both OS and DSS compared to OBS. There was no improvement in OS or DSS with the addition of a multi-agent over single-agent chemotherapy.