Clinical features

Predisposed individuals from HNPCC families have a high lifetime risk of devel oping colorectal carcinoma (70-85%), endometrial carcinoma (50%), as well as certain other cancers (below 15%) {5, 2071, 2005}. Colorectal lesions are often diagnosed at an early age (mean, 45 years), and are located in the proximal part of the colon in about two-thirds of the patients. Synchronous or metachro-nous colorectal carcinoma is present in 35% of patients. In over 90% of the cases, it shows microsatellite instability (MSI) (Table 6.04) {839, 1166, 1129}. The adenomas that occur in HNPCC tend to develop at an early age, to have villous components and to be more dysplastic than adenomas detected in the general population. Although multiple adenomas may be observed in HNPCC, florid polyposis is not a feature. Extracolonic lesions include cancer of the endometrium, renal pelvis/ureter, stomach, small bowel, ovary, brain, hepatobiliary tract, and also sebaceous tumours. Among these tumours, carcinoma of the endometrium, ureter, renal pelvis, and small bowel have the highest relative risk, and are therefore the most specific for HNPCC (Table 6.03). The occurrence of sebaceous gland tumours together with HNPCC type internal malignancy is referred to as the Muir-Torre syndrome {322}. The association of primary brain tumours (usually glioblas-

Fig. 6.62 Mucinous adenocarcinoma from a patient with HNPCC.

tomas) with multiple colorectal adenomas is referred to as the Turcot syndrome {1979}. The latter has a shared genetic basis with HNPCC on the one hand and FAP on the other hand {658}.

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