[Recognising hereditary non-polyposis colorectal cancer without a clear family history].

In 3 patients, 2 men aged 46 and 51 years and a woman aged 54 years, with colorectal cancer there was insufficient information on the basis of the family history to diagnose 'hereditary non-polyposis colorectal cancer' (HNPCC). Further investigation showed microsatellite instability in the tumour material, an indicator for a mutation in DNA-'mismatch repair' (MMR-) genes. Immunohistochemical study of lymphocytes showed an absence of the gene products MSH2 and MSH6. Study of the MMR genes revealed a pathogenic germ-line mutation in MSH2. All three patients were satisfied with genetic testing of the MMR-genes as this gave their children and their family members the opportunity to clarify genetic status. HNPCC is a clinical diagnosis, based on family history. As family history taking is often incomplete, the diagnosis is regularly not considered. The following individual criteria can help to recognize a patient at risk for HNPCC: (a) colorectal cancer diagnosed below 50 years of age, (b) second colorectal cancer, (c) a combination of colorectal and endometrial cancer.