Multicenter randomized phase II study of chemoradiation (CRT) followed by surgery (S) and chemotherapy (CT) versus induction CT followed by CRT and S in high-risk rectal cancer: GCR-3 final efficacy and safety results

4103 Background: In locally advanced RC the optimal therapeutic sequence remains an important clinical question. Induction CT prior to CRT and S may be associated with better efficacy and compliance. Methods: Eligible pts had medium or distal high risk RC defined by MRI and/or US: Tumors within 2mm of mesorectal fascia, distal T3 at/below levators, resectable T4 and T3N+. Pts, stratified by center, were randomized assigned to receive either Arm A : capecitabine (Cap) 825 mg/m2 BID 5 d/w, oxaliplatin (Ox) 50 mg/m2 IV weekly x 5 and concomitant RT: 50.4 Gy in 28 fractions. S was planned 5–6 w after CRT. Post-op four cycles of Cap 1,000 mg/m2 bid days 1 to 14; Ox 130 mg/m2 day 1 or Arm B: Induction CapOx followed by CRT and S. Two parallel, Simon 2-stage designs: α=0.05 β=0.1; 24 evaluable pts/arm 1st stage and 54 pts/arm for 2nd stage. Primary endpoint: pathological complete response (pCR). Secondary endpoints included toxicity and treatment compliance. Results: 108 Pts were randomly assigned (arm A/B, 52/5...