The mechanism of microsatellite instability is different in synchronous and metachronous colorectal cancer.

MLH1 promoter hypermethylation has been described as the primary mechanism for high-frequency microsatellite instability (MSI-H) in sporadic colorectal cancers (CRCs). The underlying molecular mechanism for microsatellite instability (MSI) in synchronous and metachronous CRCs is not well described. A total of 33 metachronous CRC patients and 77 synchronous CRC patients were identified from 2884 consecutive patients undergoing cancer surgery in an academic center.

Evidence of a preferred molecular pathway in patients with synchronous colorectal cancer.

Background: A small proportion of patients with colorectal carcinoma (CRC) have synchronous tumors at the time of diagnosis. A subset of sporadic CRCs display microsatellite instability (MSI) that is associated with MLH1 silencing due to promoter methylation. In the current study, the authors investigated the proportion of tumors with MSI in patients with synchronous colorectal carcinoma (SCRC) and the concordance in MSI status among tumors in a given individual.