Efficacy and safety of preoperative chemoradiotherapy with S-1 for advanced rectal cancer: a phase II study.

Background: Preoperative chemoradiotherapy (CRT) for patients with rectal cancer is not yet established in Japan. We aimed to evaluate the efficacy and safety of preoperative CRT with S-1, a fixed-dose combination of tegafur, gimeracil, and oteracil potassium.

Materials And Methods: We conducted a prospective, interventional, non-randomized single-center study. Radiotherapy was administered at a total dose of 45 Gy (1.8 Gy in 25 fractions) for five weeks. S-1 was administered orally for nine weeks (five weeks during and four weeks after radiotherapy) at a dose of 80 mg/m/day. The endpoint was the pathological complete response (pCR) rate.

Results: Twenty-eight patients were finally enrolled. The following patient characteristics were recorded: clinical Stage (II: n = 12, III: n = 16), median age (66 years, range 40-77 years), male/female ratio (20/8), and lesion site (Ra-Rb:3/Rb:23/Rb-P:2). Preoperative treatment was completed in 27 patients (96%). Treatment abandonment occurred because of diarrhea. Grade 3 or higher adverse events were observed in one (4%) patient with two events. No serious adverse events occurred in the ≥ 70 years group. The response rate was 68% in all patients and 68% among elderly patients. Radical resection was achieved in all patients, including 19 (68%) who underwent sphincter-preserving surgery. The pCR rate was 11% (three patients). The five-year disease-free survival rate was 68%, and the overall survival rate was 82%. Local recurrence occurred in only one patient five years after surgery.

Conclusion: Preoperative CRT with S-1 alone may be a safe and acceptable regimen from the perspective of adverse events and oncological outcomes.

Trial Registration: UMIN Clinical Trial Registry: UMIN000013598. Registered 1 April 2014, https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recpt-no=R000015887.