Phase I trial of preoperative chemoradiation therapy with S-1 for low rectal cancer.

Background/aims: A phase I study was performed to evaluate the dose-limiting toxicity and the recommended dose of the oral fluoropyrimidine S-1 when administered concurrently with radiation therapy to 9 Japanese patients with low rectal cancer.
Methodology: S-1 was given orally for a total of 9 weeks (4 weeks alone and 5 weeks during radiation therapy) at oral doses of 65 mg/m2/day (n = 3 patients) or 80 mg/m2/day (n = 6 patients). Radiation therapy was administered in 1.5 gray fractions five times weekly (Monday to Friday) for a total dose of 45 gray.
Results: All patients achieved the planned 45 gray of radiation therapy. There was no grade > or = 3 toxicity. The recommended dose of S-1 was determined to be 80 mg/m2/ day. The dose intensity of S-1 was well maintained, and the combination of S-1 plus radiation therapy was well tolerated by all patients. Sphincter-preserving procedures were possible in all but one (89%) patient. High rates of tumor shrinkage and nodular downstaging were achieved. The histological response rate was 78%, including one complete response.
Conclusions: The recommended dose of S-1 with concurrent radiation therapy was 80 mg/m2/day. Pre-operative chemoradiation therapy with S-1 was feasible and well tolerated by patients with low rectal cancer.