A multicenter randomized phase III trial of capecitabine with or without irinotecan driven by UGT1A1 in neoadjuvant chemoradiation of locally advanced rectal cancer (CinClare).

3510 Background: Our phase I/II study identified irinotecan dose differentiated by UGT1A1 genotype in the neoadjuvant CRT and showed improved pCR. The objective of this phase III study was to further investigate irinotecan combined with capecitabine-based chemoradiotherapy as preoperative treatment for locally advanced rectal cancer. Methods: We underwent a prospective, randomized, open-label, multicenter, phase 3 trial in China from Nov.2015 to Dec.2017. Eligible patients with clinical stage T3-4 and/or N+ rectal adenocarcinoma were randomly allocated to two arms. The approach in control arm (Arm A, n = 180) was pelvic radiation of 50 Gy/25 fractions with concurrent capecitabine 825 mg/m 2 twice daily 5 days per week, followed by a cycle of XELOX two weeks after the end of CRT. The experimental arm (Arm B, n = 180) was pelvic radiation with capecitabine 625 mg/m 2 twice daily 5 days per week and combined with weekly irinotecan. The irinotecan dose was used based on UGT1A1 genotype of 80mg/m 2 for UGT1A1*1*1 or 65mg/m 2 for UGT1A1*1*28 weekly, followed by a cycle of XELIRI. The primary endpoint is pathological complete response (pCR). This trial was registered with ClinicalTrials.gov, number NCT02605265. Results: Surgery was performed in 86.5% and 88.2% of patients in two groups, with 38.9% and 30.5% of patients got abdominoperineal resection respectively. The pCR rate was 17.5% in Arm A and 33.8% in Arm B (P = 0.001). Four and 6 patients maintained a complete clinical response status at least 12 months and were marked as cCR. The CR rate, including pCR and cCR, was 17.4% in Arm A and 33.1% in Arm B (P = 0.001). The most common grade 3-4 adverse events during preoperative treatment were leucopenia (3.4% vs. 25.3%), neutropenia (1.7% vs. 19.7%) and diarrhea (1.7% vs. 13.5%) in two arms. The overall rate of surgical complications were not significantly different between arms (11.0% vs. 14.6%). Conclusions: Adding irinotecan guided by UGT1A1 to capecitabine-based neoadjuvant chemoradiotherapy significantly increases complete tumor response. The treatment toxicities were increased but tolerable. This treatment can be as an option for ‘watch and wait’ approach. Clinical trial information: NCT02605265.