Hereditary nonpolyposis colon cancer (HNPCC) is the most common autosomal dominantly inherited cancer syndrome that predisposes to colorectal cancer (CRC).
1,2 Estimates of its frequency range from 2% to as much as 7% of the total CRC burden.
2-5 Colorectal cancer occurs at an early age (mean age, about 44 years), with right-sided predominance (approximately 70% of tumors are proximal to the splenic flexure)
1,2,6 and a significant occurrence of synchronous and metachronous lesions.
2,7 There is an excess of extracolonic cancers, the most common of which is carcinoma of the endometrium, followed by cancers of the ovary, stomach (particularly in Asian countries such as Japan and Korea), small bowel, pancreas, hepatobiliary tract, and brain, and transitional cell carcinoma of the upper uroepithelial tract.
8,9 Some families also have phenotypic manifestations such as sebaceous adenomas or sebaceous carcinomas consistent with the Muir-Torre syndrome.
2,10-16 Profuse colonic adenomas consonant with classic familial adenomatous polyposis and its attenuated variant must be excluded in the medical evaluation of patients at high risk for HNPCC.
1,2