A Randomized Phase 2 Study of Neoadjuvant Chemoradiaton Therapy With 5-Fluorouracil/Leucovorin or Irinotecan/S-1 in Patients With Locally Advanced Rectal Cancer.

Purpose: The purpose of this study was to evaluate the rate of pathologic complete response (pCR) in patients with locally advanced rectal cancer (LARC) treated with neoadjuvant chemoradiation therapy (CRT) with leucovorin (FL) versus irinotecan/S-1 (IS).

Methods And Materials: Patients with resectable LARC (clinical stage T3/4, lymph node positive, or both) were randomly assigned to receive preoperative radiation (45-50.4 Gy in 25 to 28 daily fractions) and concomitant chemotherapy either with a bolus injection of FL (400 mg/m(2)/day 5-fluorouracil and 20 mg/m(2)/day leucovorin) for 3 consecutive days every 4 weeks for 2 cycles (FL group) or with 40 mg/m(2) irinotecan on days 1, 8, 15, 22, and 29, and 35 mg/m(2) S-1 twice on the day of irradiation (IS group). Curative surgery was performed approximately 4 to 8 weeks after the completion of CRT. The postoperative chemotherapy regimen was FL with a primary endpoint of a pCR rate evaluation.

Results: One hundred forty-two eligible patients were randomly assigned, and the median follow-up duration was 43.8 months (95% confidence interval, 40.8-46.8 months). One hundred thirty-three patients (93.7%) of 142 underwent total mesorectal excision; pCR was achieved in 11 (16.7%) of 66 patients in the FL group and 17 (25.8%) of 67 patients in the IS group (P=.246). When good responders were defined as patients with Mandard grades 1 and 2, the rate of good responders was significantly higher in the IS group than in the FL group (54.6% vs 36.4%, respectively, P=.036). The preoperative rates of grade 3 and 4 toxicities were higher in the IS group (7.0%) than in the FL group (1.4%, P=.095). The 3-year disease-free survival was not significantly different between the 2 groups (79.7% vs 76.6%, respectively, P=.896).

Conclusions: IS-based preoperative CRT did not increase pCR rate, but it did increase acute toxicities compared with standard 5-FU treatment. Therefore, further investigation is needed.