Hereditary Nonpolyposis Colon Cancer Hereditary nonpolyposis colon cancer (HNPCC), also known as Lynch syndrome, is another autosomal dominant trait. It is characterized by the presence of three or more relatives with histologically documented colorectal cancer, one of whom is a first-degree relative of the other two; one or more cases of colorectal cancer diagnosed before age 50 in the family; and colorectal cancer involving at least two generations. In contrast to polyposis coli, HNPCC is associated with an unusually high frequency of cancer arising in the proximal large bowel. The median age for the appearance of an adenocarcinoma is. | Chapter 087. Gastrointestinal Tract Cancer Part 9 Hereditary Nonpolyposis Colon Cancer Hereditary nonpolyposis colon cancer HNPCC also known as Lynch syndrome is another autosomal dominant trait. It is characterized by the presence of three or more relatives with histologically documented colorectal cancer one of whom is a first-degree relative of the other two one or more cases of colorectal cancer diagnosed before age 50 in the family and colorectal cancer involving at least two generations. In contrast to polyposis coli HNPCC is associated with an unusually high frequency of cancer arising in the proximal large bowel. The median age for the appearance of an adenocarcinoma is 50 years 10-15 years younger than the median age for the general population. Despite having a poorly differentiated histologic appearance the proximal colon tumors in HNPCC have a better prognosis than sporadic tumors from patients of similar age. Families with HNPCC often include individuals with multiple primary cancers the association of colorectal cancer with either ovarian or endometrial carcinomas is especially strong in women. It has been recommended that members of such families undergo biennial colonoscopy beginning at age 25 years with intermittent pelvic ultrasonography and endometrial biopsy for afflicted women such a screening strategy has not yet been validated. HNPCC is associated with germline mutations of several genes particularly hMSH2 on chromosome 2 and hMLHl on chromosome 3. These mutations lead to errors in DNA replication and are thought to result in DNA instability because of defective repair of DNA mismatches resulting in abnormal cell growth and tumor development. Testing tumor cells through molecular analysis of DNA or immunohistochemical staining of paraffin-fixed tissue for microsatellite instability sequence changes reflecting defective mismatch repair in patients under age 50 with colorectal cancer and a positive family history for colorectal or endometrial .
