Sub-millimeter surgical margin is acceptable in patients with good tumor biology after liver resection for colorectal liver metastases.

BACKGROUND: The definition of R1 resection in colorectal cancer liver metastases (CRLM) remains debatable. This retrospective study was conducted to clarify the impact of R1 margin on patient survival after liver resection for CRLM, taking into consideration tumor biology, including RAS status and chemotherapy response. METHODS: We retrospectively analysed the clinical and survival data of 214 CRLM patients with initially resectable liver metastases who underwent liver resection after receiving neoadjuvant chemotherapy between January 2006 and December 2016. RESULTS: R1 resection significantly impacted patients' overall survival (OS) and disease-free survival (DFS) in the overall patient cohort (5-year OS: 53.2% for R0 vs 38.2% for R1, P = 0.001; 5-year DFS: 26.5% for R0 vs 10.5% for R1, P = 0.002). In the RAS wild-type subgroup and respond to chemotherapy (RC) subgroup, R1 reached a similar OS to those who underwent R0 resection (RAS wild-type, P = 0.223; RC, P = 0.088). For the RAS mutated subgroup and no response to chemotherapy (NRC) subgroup, OS was significantly worse underwent R1 resection (RAS mutant, P = 0.002; NRC, P = 0.022). When considering tumor biology combining RAS and chemotherapy response status, R1 resection was only acceptable in patients with both RAS wild-type and RC (5-year OS: 66.4% for R0 vs 65.2% for R1, p = 0.884), but was significantly worse in those with either RAS mutation or NRC. CONCLUSIONS: Tumor biology plays an important role in deciding the appropriate resection margin in patients with CRLM undergoing radical surgery. R1 resection margin is only acceptable in RAS wild-type patients who respond to chemotherapy.