[Genomic instability analysis in hereditary cancer syndrome]

The discovery of microsatellite instability (MSI) and its association to hereditary nonpolyposis colorectal cancer (HNPCC) in 1993 gave rise to a new criterion in tumor biology. By using five microsatellite markers, colorectal carcinomas (CRC) may be classified either as high frequency-MSI (MSI-H) if two or more of the five markers show instability, or as low frequency-MSI (MSI-L)/microsatellite stable (MSS) if one or less shows instability. MSI-H tumors which comprise about 15% of total CRC show distinctive clinicopathologic features: proximal colon location, mucinous and undifferentiated histology, presence of tumor-infiltrating lymphocytes, and a less aggressive clinical course. Mismatch repair gene mutations, transcription loss of a mismatch repair gene associated with promoter region hypermethylation, or loss of imprinting have been proposed as some of the causes for MSI.