543PThe impact of completeness of chemotherapy on the efficacy of irinotecan in the preoperative chemoradiotherapy of (CRT) locally advanced rectal cancer

Abstract Background The purpose of this study was to explore the impact of completeness of weekly irinotecan combined with capecitabine-based preoperative chemoradiotherapy in patients with locally advanced rectal cancer (LARC). Methods LARC patients receiving neoadjuvant CRT between May 2011 and February 2018 were enrolled. The paradigm included preoperative pelvic RT (50 Gy/25Fx) concurrently with capecitabine (625 mg/m2, bid, d1-5) and irinotecan (80 mg/m2 for UGT1A1*1*1 genotype or 65 mg/m2 for UGT1A1*1*28 genotype, qw), followed by a course of XELIRI and surgery. The actual cycles of concurrent irinotecan delivered was reviewed from the electronic records. Patients were divided into the low-completeness group (1∼3 cycles) and the high-completeness group (4∼5 cycles). Univariate and multivariate analyses were performed to identify risk factors of the completeness. A nomogram was built to divide patients into 3 groups with different risk. Results A total of 371 patients were enrolled, with 102 patients from a phase III clinical trial (CinClare, NCT02605265). The proportion of patients with low completeness was 32.4% versus 67.6% with high completeness in the CinClare group, and 41.3% versus 58.7% in the remaining group (p = 0.12). In the CinClare group, the complete response (CR) rate was 24.2% in the low-completeness patients versus 42.6% in the high-completeness patients (p = 0.07). The difference was more significant in the general population (28.6% vs 71.6%, p = 0.02). Univariate analysis showed age over 60, female, anemia at baseline, and a low pretreatment pre-Alb level were associated with a low completeness. By using multivariate analysis and building a nomogram, we could divide patients into 3 groups: (1) high-risk group (risk score>200); (2) intermediate-risk group (score 100∼200); (3) low-risk group (score≤100). The rates of high completeness in the 3 groups were 27.8%, 47.6% and 69.5%, respectively. Conclusions Our analysis suggested a higher completeness of weekly irinotecan was associated with a higher CR rate. Comprehensive evaluation of the patient performance is necessary before starting the intensified treatment. Legal entity responsible for the study The authors. Funding Has not received any funding. Disclosure All authors have declared no conflicts of interest.