The value of microsatellite instability in the detection of HNPCC families and of sporadic colorectal cancers with special biological features: An investigation on a series of 100 consecutive cases

Background: Microsatellite instability (MI) is a biological characteristic of most tumors involved in hereditary non polyposis colorectal cancer (HNPCC). This disease appears to be caused by germline mutations in mismatch repair (MMR) genes, which are responsible for repairing single base-pair mismatches. At least five human genes participate in MMR. MI also occurs in 10%-15% of sporadic colorectal cancers. Because MI detection has been suggested as an alternative diagnostic tool for identification of HNPCC families, in this study we analyzed the MI pattern in 100 consecutive colorectal carcinomas in order to correlate them with the clinicopathologic features and family histories of the patients. Patients and methods: A series of 100 colorectal cancers was evaluated for MI with 10 polymerase chain reaction primer sets. Instability results were compared with family history and other clinical and biological characteristics. Results: MI was detected in 36 of 100 cancers, 27 of which showed low instability and nine a high instability. The low- and high-instability cases showed similar clinicopathological characteristics, and significantly positive associations were observed between MI and mucinous histological type (P = 0.0001) and MI and peritumoral lymphocytic infiltration (P = 0.01). A single HNPCC family was identified in the high-grade MI group, while two families belonged to the MI-negative group. Conclusions: Our data suggest that MI screening is probably not an efficient strategy for identifying HNPCC cases. MI does, however, appear capable of defining a category of colorectal cancers with favourable prognostic features and should be investigated at least in all cases of mucinous adenocarcinomas.