Microsatellite instability of cancers and concomitant adenomas in synchronous multiple colorectal cancer patients

The precise role of microsatellite instability (MSI) in the development of multiple colorectal cancers has not been elucidated. In the present study, the authors examined MSI and the clinicopathological features of both cancers and concomitant adenomas in nonfamilial multiple synchronous colorectal cancer (multiple CC) patients. Fifty adenomas and 108 cancers were obtained from the surgically resected specimens of 51 multiple CC patients. Nine microsatellite markers were used to determine MSI by polymerase chain reaction (PCR). The frequency of MSI-H adenomas in multiple CC patients was higher than that in single CC patients, while MSI-H frequency of cancers was similar to that in single CC patients. There was a tendency that, in multiple CC patients, when a patient has an MSI-H adenoma, he/she also has MSI-H cancer. The clinicopathological features of multiple CC were similar to those of single CC except the ratio of mucinous cancer and concomitant adenomas. According to this study, in some multiple CC patients, genetic instability seems to play an important role in the development of cancers as well as adenomas. We regard MSI testing for multiple CC patients is useful to distinguish "MSI-related" multiple CC from "MSI-unrelated" multiple CC, and MSI-related multiple CC should be followed up carefully as hereditary nonpolyposis colorectal cancer (HNPCC) patients.