Background: Hereditary non-polyposis colorectal cancer (HNPCC) patients frequently develop synchronous colorectal cancer (SCRC) which also occurs sporadically in other patients. Recent studies on microsatellite instability (MSI) in sporadic SCRC diverge completely in their findings (0%-100%). In the present study MSI and mismatch repair (MMR) proteins were evaluated according to standardised criteria (exclusion of a family history, MSI analysed according to NCI recommendations)
Methods: Paraffin embedded sections of SCRC of 30 patients were evaluated for MSI and the loss of protein expression of hMLH1 and hMSH2.
Results: 3 out of 30 (10%) patients exhibited MSI-H which 5 out of 30 (17%) showed MSI-L. Loss of protein expression of either hMLH1 or hMSH2 was found in all cases of MSI-H and none of the MSI-L cancers.
Conclusion: MSI is found in sporadic cases of SCRC to about the same extent as it is mentioned in the literature on sporadic single colorectal cancers. Immunohistochemistry with mismatch repair proteins could be used as a pre-screening for MMR deficiency in sporadic SCRC.