Summary

Colorectal cancer (CRC) is a significant cause of mortality in Western populations. About 15 % of CRC patients report a family history of the disease. Studies on individuals with a genetic predisposition to CRC have been responsible for sig-nificant advances in the understanding of this disease. Thus, although developments in molecular biology have been mainly restricted to a minority of individuals with a hereditary back-ground, information obtained from this group may affect the diagnosis and therapy of sporadic CRCs as well. Deficiency in the DNA mismatch repair (MMR) system results in microsatellite instability (MSI). Individuals from hereditary non-polyposis colorectal cancer (HNPCC) kindreds with germline mutations in genes involved in MMR may benefit from clinical screening programs. The higher frequency of MSI in HNPCC than in sporadic tumours suggests that involvement of MMR genes in sporadic adenomas may be uncommon. Consequently, MSI in adenomas could be a useful tool for HNPCC screening in the general population. Moreover, infor-mation gained from this subset of patients may aid in selecting appropriate endoscopic surveillance regimens, and in predict-ing the prognosis and response to treatment in patients with sporadic CRC exhibiting MSI. The purpose of this review is to discuss MSI and its clinical applications in colorectal malignancies, focusing on the HNPCC syndrome