Background: We have reported that neoadjuvant chemotherapy (NACT) with FOLFIRINOX followed by chemoradiotherapy (CRT), surgery, and adjuvant chemotherapy (ACT) significantly improved outcomes in patients (pts) with locally advanced rectal cancer (LARC) compared with pts who received standard CRT, surgery, and ACT. We now report the primary and secondary endpoints with mature follow-up (F/U). Methods: PRODIGE 23 is a phase III randomized clinical trial. Eligible pts had cT3 or cT4, M0 rectal adenocarcinomas <15 cm from the anal verge, age 18-75 years, and WHO PS ≤1. Randomization was stratified by center, T stage, N status, T location, and T extramural spread. Arm A pts received preoperative CRT (50 Gy, 2 Gy/fr; 25 fr + capecitabine), surgery, then ACT for 6 months (mos). Arm B pts received 6 cycles of mFOLFIRINOX, then the same preoperative CRT, surgery and 3 mos of ACT, mFOLFOX6 or capecitabine. From 6/2012 to 6/2017, pts were randomly assigned in Arm A (n=230) and B (n=231) by 35 participating centers. Analysis was performed on intent-to-treat population. For survival outcomes, HR and 95% CI were estimated by a stratified Cox proportional hazard (PH) model. However, we observed non-PH. So we used the restricted mean survival time (RMST) to evaluate the treatment effect (Liang F & al Ann Oncol 2018, Pak K & al JAMA Oncol 2017). Results: With a median F/U of 82.2 mos, death was reported for 55 pts in arm A and 42 in Arm B. All survival endpoints were better for Arm B vs Arm A. The absolute increase in 5-year survival were 7.6% for Disease-Free Survival (DFS), 6.9% for Overall Survival (OS), 9.9% for Metastasis-Free Survival (MFS), and 5.7% for Cancer Specific Survival (CSS) in Arm B compared to Arm A. Survival results at 7 years are presented in the Table. 7-year cumulative incidence of locoregional relapses are 5.3% in arm B vs 8.1% in arm A (p= 0.38). Conclusions: NACT with mFOLFIRINOX followed by CRT, surgery, and ACT significantly improved all outcomes, including OS in pts with LARC vs those who received standard CRT, surgery, and ACT. Clinical trial information: NCT01804790.

CI= Confidence Interval * at 84 mos F/U.