Hereditary Nonpolyposis Colorectal Cancer Syndrome

HNPCC, or Lynch II syndrome occurs in families affected by a combination of early-onset colon cancer and cancers of the ovary, endometrium, stomach, small bowel, pancreas, bile ducts, skin (sebaceous adenomas and carcinomas), and urinary tract. HNPCC accounts for only 2% of cases of hereditary ovarian cancer, and 5% of all colorectal cancers. Cancer susceptibility in these families is transmitted in an autosomal dominant fashion, and penetrance varies. By the age of 65, approx 70% of carriers will develop colorectal cancer (128,129). Affected members tend to present with early-onset colorectal cancers (diagnosis before age 45), and have a tendency toward proximal tumors. Synchronous and metachronous cancers are common.

Following colorectal cancer, endometrial cancer is the second most common malignancy in these families. In fact, in a large family-based study conducted by Aarnio et al. (130) the incidence of endometrial cancer was more than the incidence of colorectal cancer in women (60% vs 54%, respectively). A population-based study noted similar results (42% vs 30%, respectively) (131). Patients with HNPCC incur a 3.5-8-fold increased risk of ovarian cancer (132,133), and lifetime risks vary between 9 and 12% (129,130). Ovarian cancer risk is particularly associated with mutations in MSH2 (132).

Other noncolonic primaries occur with varying frequencies. Lifetime risks for gastric, biliary, and urinary tract primaries are 13-19%, 18%, and 10%, respectively (129,130). For other tumors, the risk is less than 4% (130). The majority of HNPCC carriers who develop colon cancer will also develop a second primary, usually a synchronous or metachronous colon cancer, or endometrial cancer. After the diagnosis of colorectal cancer, the risk of any metachronous cancer reached 90%. After the diagnosis of endometrial cancer, the risk reached 75%. The most common second tumor was a new colorectal cancer or endometrial cancer (129).

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