A phase i trial of S-1 with concurrent radiotherapy in patients with locally recurrent rectal cancer

Background: The purpose of this phase I trial of S-1 chemotherapy in combination with pelvic radiotherapy for locally recurrent rectal cancer was to determine the maximum tolerated dose (MTD), recommended dose (RD), and dose-limiting toxicity (DLT) of S-1. Methods: We enrolled 9 patients between April 2005 and March 2009. Radiotherapy (total dose, 60 Gy in 30 fractions) was given to the gross local recurrent tumor and pelvic nodal metastases using three-dimensional radiotherapy planning. We administered oral S-1 twice a day on days 1-14 and 22-35 during radiotherapy. The dose of S-1 was initially 60 mg/m²/day and was increased to determine the MTD and RD for this regimen. Results: DLT appeared at dose level 2 (70 mg/m²/day) in 2 patients, who experienced grade 3 enterocolitis and consequently required suspension of S-1 administration for longer than 2 weeks. Hematological toxicity was mild and reversible. At the initial evaluation, complete regression and partial regression were seen in 1 patient (11%) and 2 patients (22%), respectively. Conclusion: This phase I trial of S-1 chemotherapy with pelvic radiotherapy for locally recurrent rectal cancer revealed that the MTD for S-1 was 70 mg/m²/day and the RD was 60 mg/m²/day.