Phase 2 study of perioperative chemotherapy with SOX and surgery for stage III colorectal cancer (SOS3 study).

This phase 2 study evaluated the safety and efficacy of perioperative chemotherapy with S-1 plus oxaliplatin (SOX) for stage III colorectal cancer (CRC). Patients with stage III CRC received surgery after neoadjuvant chemotherapy (NAC; SOX 4 cycles) and adjuvant chemotherapy (AC; SOX 4 cycles). The primary endpoints were response rate and safety. We enrolled 30 patients. Their median age was 62 years (range: 43-87 years); 53% were women. They received a median of 4 cycles (range: 1-4) of NAC and a median 4 cycles (range: 0-4) of AC. Five patients interrupted NAC treatment because of toxicity (grade 3 diarrhoea [n = 1], grade 3 ileus [n = 1], and grade 3-4 thrombocytopenia [n = 3]). Patients' responses were complete responses: n = 2 (6.6%), partial responses: n = 21 (70%), stable disease: n = 6 (20.0%), and progressive disease: n = 1 (3.3%; response rate: 73.3%). Curative resection was performed in 29 patients. No patients showed anastomotic leakage. Five-year overall survival and disease-free survival were 83.3% and 76.7%, respectively (median follow-up time: 48 months). NAC using SOX regimen is safe and effective, and may lead to reduced local recurrence and distant metastasis. Long-term outcomes are awaited to evaluate further the efficacy of this strategy (UMIN000006790).