Clinicopathologic features and prognosis of synchronous and metachronous multiple primary colorectal cancer.

PURPOSE Multiple primary colorectal cancers (MPCCs) are different from solitary colorectal cancers in many aspects, which are not well studied. The aim of this study was to clarify the clinicopathological features and prognosis of MPCCs. METHODS The data of 64 patients with MPCCs out of 2300 patients with colorectal cancers (CRCs) from January 2009 to December 2017 were retrospectively analyzed. Stratified analysis was conducted based on subtypes and microsatellite status. RESULTS The overall incidence of MPCC was 2.8% and the median follow-up duration was 51.5 (range 1-120) months. Metachronous CRCs (MCRCs) are more likely to appear in the right colon (p < 0.05). However, no significant differences regarding age, sex, BMI, tumor size, smoking/drinking history, TNM stage, family history of cancer, and 5-year survival rate were observed between synchronous CRC (SCRC) and MCRC. Advanced TNM stage (III) and the presence of polyps were found to be independent poor prognostic factors for MPCCs. The prevalence of mismatch repair deficiency (dMMR) in MPCCs was 28.1%. Deficient MMR is more likely to appear in younger, lighter MPCC patients with polyps (p < 0.05). Of four mismatch repair proteins, MLH-1, MSH-2, MSH-6, and PMS-2 were negative in nine, nine, five, and nine patients, respectively. The 5-year survival rate did not differ significantly between MMR-proficient (pMMR) and dMMR groups (p = 0.752). CONCLUSIONS Synchronous CRC (SCRC) and MCRC might represent similar disease entities with different courses. Deficient MMR is more likely to appear in younger, lighter MPCC patients with polyps and it is an essential indicator for screening Lynch syndrome.