Synchronous and metachronous colorectal cancers: distinct disease entities or different disease courses?

Background/aims: This study aimed to investigate the clinicopathological characteristics of synchronous and metachronous colorectal cancers (CRCs).

Methodology: From January 1, 2001 to December 31, 2010, 5898 patients who underwent surgical resection for CRCs were enrolled. Synchronous CRC was defined as presence of more than one primary CRC within 6 months of resection of the primary tumor; while CRC that occurred at least 6 months later was regarded as metachronous CRC.

Results: 5346 patients were eligible for the study and divided into three groups: solitary, synchronous and metachronous CRC. The overall prevalence of the synchronous CRC was 2.2% and the 10-year cumulative incidence of metachronous cancer was 0.84%. 29 (64%) metachronous cancers were diagnosed within 3 years of the index cancer and the mean time interval was 3.2 years. Male gender and presence of associated adenoma were significant risk factors for both synchronous and metachronous CRC. Synchronous and metachronous CRC patients shared similar clinicopathological features except that the former were older than the latter by 3.7 years. The five-year survival rates were not different among the three groups.

Conclusions: Our study indicates that synchronous and metachronous CRC might represent similar disease entity with different courses.