The high recurrence rate of colorectal cancer liver metastasis (CRCLM) after surgery remains a crucial problem. However, adjuvant chemotherapy after hepatectomy for CRCLM has not yet been established. This study evaluated the efficacy of adjuvant therapy with S-1 and oxaliplatin (SOX).

In a multicenter, randomized, phase II study, patients undergoing curative resection of CRCLM were randomly enrolled in a 1:1 ratio to either the low- or high-dose group. S-1 and oxaliplatin were administered from days 1 to 14 of a 3-week cycle as a 2-h infusion every 3 weeks. The dose of S-1 was fixed at 80 mg/m2. The doses in the low- and high-dose oxaliplatin groups were 100 mg/m2 (low-dose group) and 130 mg/m2 (high-dose group), respectively. This treatment was repeated eight times. The primary endpoint was the rate of discontinuation owing to toxicity. The secondary endpoints were the relapse-free survival (RFS) and frequency of adverse events (AEs).

Between August 2010 and March 2015, 44 patients (low-dose group: 31 patients and high-dose group: 13 patients) were enrolled in the study. Of these, one patient was excluded from the efficacy analysis. In the high-dose group, five of nine patients were unable to continue the study due to toxicity in February 2013. At that time, recruitment to the high-dose group was stopped from the protocol. The relative dose intensity (RDI) for S-1 in the low- and high-dose groups were 49.8 and 48.7% (p = 0.712), and that for oxaliplatin was 75.9 and 73.0% (p = 0.528), respectively. The rates of discontinuation due to toxicity were 60 and 53.8% in the low- and high-dose groups, respectively, with no marked difference noted between the groups (p = 0.747). The frequency of grade ≥ 3 common adverse events was neutropenia (23.3%/23.1%), diarrhea (13.3%/15.4%), and peripheral sensory neuropathy (6.7%/7.7%). The disease-free survival (DFS) at 3 years was 52.9% in the low-dose group, which was not significantly different from that in the high-dose group (46.2%; p = 0.705).

SOX regimens as adjuvant therapy after hepatectomy for CRCLM had high rates of discontinuation due to toxicity in both groups. In particular, the RDI of S-1 was < 50%. Therefore, the SOX regimen is not recommended as adjuvant chemotherapy after hepatectomy for CRCLM.