Higher incidence of metachronous advanced neoplasia in patients with synchronous advanced neoplasia and left-sided colorectal resection for colorectal cancer

Background and Aims: There is an increased risk of developing metachronous colorectal cancer (CRC) in the remnant colorectum after surgical resection of CRC. We evaluated the incidence of metachronous advanced neoplasia (AN) after surgery for CRC according to resection type and synchronous AN. Methods: This cohort study included patients who underwent surgical resection for initial CRC at a tertiary cancer center in Japan between September 2002 and December 2012. The cumulative probability of metachronous AN was calculated using the Kaplan-Meier method and was evaluated by the log-rank test. Results: Metachronous AN was detected in 145 of 1731 included patients, and the 5-year cumulative probability of metachronous AN was 13.1%. There was no significant difference in the incidence of metachronous AN in the right-sided colorectal resection versus left-sided colorectal resection (LCR) groups (log-rank test P = .151), whereas the incidence of metachronous AN was significantly higher in patients with synchronous AN (log-rank test P<.001). In subgroup analysis of patients according to resection type and synchronous AN, the LCR group with synchronous AN showed a significantly higher incidence of metachronous AN than the other groups (log-rank test P<.001). Conclusions: We found that synchronous AN, but not resection type, was independently associated with the incidence of metachronous AN in patients who underwent surgical resection of CRC. In addition, subjects with synchronous AN after LCR had a potentially increased risk for metachronous AN. Thus, it may be useful to perform risk stratification according to synchronous AN and resection type.