[Clinical aspects of hereditary nonpolyposis colorectal cancer: experience of genetic consultation].

Five-ten percent of early-onset (up to age of 50) colorectal cancers are regarded as being inherited. Positive results of a medical genetic examination call for microsatellite instability test. However, that method is not absolutely reliable because although all microsatellite instability tests for hereditary nonpolyposis colorectal cancer are positive, microsatellite instability of tumor DNA occurs in 15% of sporadic colorectal carcinoma. Moreover, Russian diagnostic practices are peculiar in that "familial history" is often missed due to premature demise of relatives and lack of data. Under the circumstances, research should be focused on issues of still earlier onset of cancer as well as multifocal nature of tumor growth although similar manifestations may occur in sporadic cancer.