An early phase II trial of S-1 in Japanese patients with cytokine-refractory metastatic renal cell carcinoma

S-1, an oral anticancer agent, contains tegafur (FT), 5-chloro-2,4-dihydroxypyridine (CDHP), and potassium oxonate (Oxo) at a molar ratio of FT:CDHP:Oxo = 1:0.4:1. The aim of this trial was to investigate the efficacy and safety of S-1 in Japanese patients with cytokine-refractory metastatic renal cell carcinoma (RCC). We conducted a non-randomized, open-label trial in Japanese patients with metastatic RCC who had received nephrectomy and had failed cytokine-based immunotherapy. The primary endpoint was response rate. S-1 40-60 mg based on the body surface area was administered twice daily (80-120 mg/day) for 4 consecutive weeks, followed by a 2-week rest period; cycles were repeated every 6 weeks. Patients continued treatment until disease progression, unacceptable toxicity, or withdrawal of consent. A total of 20 eligible patients were enrolled. Among these, 3 patients had partial response, yielding objective response rate of 15%; 13 patients had no change; 4 patients had progressive disease. The median time-to-progression and median overall survival were 12.0 and 25.7 months, respectively. The initial adverse event was generally mild to moderate in severity. The most common grade 3/4 drug-related hematological and non-hematological adverse events were neutropenia (20.0%) and anorexia (20.0%), respectively. S-1 is active and well tolerated for the treatment of cytokine-refractory metastatic RCC.