Phase I trial of neoadjuvant concurrent chemoradiotherapy with S-1 and weekly irinotecan in locally advanced rectal cancer.

S-1 is a novel, oral fluoropyrimidine and a known radiosensitizer. We conducted a phase I trial to establish a schedule of S-1/irinotecan with standard pelvic radiotherapy as a preoperative treatment of locally advanced rectal cancer. Our findings suggest that this new combination is feasible and well tolerable.