LAUSR

Background The survival benefit of and indications for adjuvant chemotherapy (AC) for colorectal liver metastases (CRLM) remain unclear. Methods Patients who were diagnosed with liver-limited CRLM between 2005 and 2007 and subsequently underwent R0 resection without preoperative chemotherapy were identified in a Japanese nationwide survey. This overall cohort was divided into synchronous and metachronous CRLM cohorts. In each of the three cohorts, the patients that were given AC were matched with those treated with surgery alone via 1:1 propensity score (PS) matching. Recurrence-free survival (RFS) and overall survival (OS) after the initial hepatectomy were compared. Results The median follow-up period was 79.4 months and the overall, synchronous, and metachronous cohorts included 1145, 498, and 647 patients, respectively. After the PS matching, the patients’ demographics were well balanced. AC was effective in terms of both RFS and OS in the overall cohort (RFS hazard ratio [HR] 0.784, p  = 0.045; OS HR 0.716, p  = 0.028) and synchronous cohort (RFS HR 0.677, p  = 0.027; OS HR 0.642, p  = 0.036), whereas AC was not effective in the metachronous cohort (RFS HR 0.875, p  = 0.378; OS HR 0.881, p  = 0.496). However, in the metachronous cohort, AC was effective in terms of OS in the subgroup that exhibited disease-free intervals of ≤ 1 year after primary tumor resection (RFS HR 0.667, p  = 0.068; OS HR 0.572, p  = 0.042). Conclusion Adjuvant chemotherapy has a survival benefit for patients with resected CRLM. Synchronous CRLM is a favorable indication for AC, whereas in metachronous CRLM, the use of AC should be individualized according to each patient’s risk factors.