OBJECTIVETo investigate the incidence of microsatellite instability (MSI) in sporadic colorectal carcinoma (CRC) using BAT-25 and BAT-26 loci, and its association with clinicopathological features.

METHODSMicrosatellite analysis was performed on tissue samples from 73 primary and 53 metastatic tumors collected at the Department of Pathology, Fudan University Cancer Hospital in 2002. Genomic DNA was extracted from paraffin-embedded tissues. Microsatellite alterations of BAT-25 and BAT-26 were detected using fluorescent PCR followed by fragment analysis on automatic DNA sequencer with GeneScan 3.1 software. A case of hereditary nonpolyposis colorectal cancer syndrome (HNPCC) with known high-frequency MSI (MSI-H) was included as positive control.

RESULTSEleven out of 73 samples from primary tumors (15.1%) were MSI-positive and significantly associated with patient age, tumor site, differentiation and prognosis (P < 0.05). There was no significant difference between the positive rate of MSI in tissue samples from primary and metastatic sites among the 53 metastatic tumors, being 17.0% and 13.2%, respectively, P > 0.05. Two cases with negative MSI at the primary site but positive at the metastatic sites were observed.

CONCLUSIONMSI is a frequent molecular event that may serve as a useful parameter for studying tumor biological behavior. MSI plays a partial role in the metastasis of sporadic CRC, but the role of mismatch repair genes and its exact mechanism remains to be determined. The classification of sporadic CRC according to MSI may be of importance both theoretically and practically.