30 June 2005
Hereditary Nonpolyposis Colorectal Cancer (HNPCC) is the most common form of familial colorectal cancer and accounts for 1-3% of all colorectal tumours. It is diagnosed following established guidelines, the most recent version being the Revised Bethesda Guidelines for HNPCC (Lynch Syndrome) and Microsatellite Instability [Umar A et al. (2004) J Natl Cancer Inst 96, 261-268]. These guidelines update the original Bethesda Guidelines of 1997 on testing individuals with apparent HNPCC for microsatellite instability, or MSI. This is a genetic feature of tumours that have lost DNA mismatch repair (MMR) activity, mostly due to mutations in the MSH2 or MLH1 genes, although additional genes can also be involved. Such mutations generally cause abnormal MSH2 or MLH1 protein expression, which can be detected by immunostaining.
The purpose of testing for HNPCC is to identify individuals in whom colorectal cancer has arisen due to inherited, strongly disease-predisposing mutations. A diagnosis of HNPCC has implications for the individual