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Hereditary nonpolyposis colorectal cancer, often called HNPCC or Lynch syndrome, is a type of inherited cancer of the digestive tract, particularly the colon (large intestine) and rectum. People with hereditary nonpolyposis colorectal cancer have an increased risk of cancers of the stomach, small intestine, liver, gallbladder ducts, upper urinary tract, brain, skin, and prostate. Women with this disorder also have a greatly increased risk of endometrial and ovarian cancer. Even though the disorder is described using the term nonpolyposis, people with hereditary nonpolyposis colorectal cancer may have occasional noncancerous growths called colon polyps. These colon polyps occur at an earlier age than do colon polyps in the general population. Although the polyps do not occur in greater numbers than in the general population, they are more prone to become cancerous.
In the United States, about 160,000 new cases of colorectal cancer are diagnosed each year. Hereditary nonpolyposis colorectal cancer is responsible for approximately 2 percent to 7 percent of all diagnosed cases of colorectal cancer.
Variations of the MLH1, MSH2, MSH6, and PMS2 genes increase the risk of developing hereditary nonpolyposis colorectal cancer.
All of these genes are involved in the repair of mistakes made when DNA is copied (DNA replication) in preparation for cell division. Mutations in any of these genes prevent the proper repair of DNA replication mistakes. As the abnormal cells continue to divide, the accumulated mistakes can lead to uncontrolled cell growth and possibly cancer. Although mutations in these genes predispose individuals to cancer, not all people who carry these mutations develop cancerous tumors.
Hereditary nonpolyposis colorectal cancer risk is inherited in an autosomal dominant pattern, which means one inherited copy of the altered gene is sufficient to increase cancer risk. It is important to note that people inherit an increased risk of cancer, not the disease itself. Not all people who inherit mutations in these genes will develop cancer.
'''Hereditary nonpolypsis colorectal cancer''' (HNPCC) is characterized by an increased risk of colon cancer and other cancers such as endometrium, ovary, stomach, small intestine, hepatobiliary tract, upper urinary tract, brain, and skin. Individuals with HNPCC have about a 80% lifetime risk for colon cancer. Two-thirds of these cancers occur in the proximal colon. The mean age of colorectal cancer diagnosis is 44. Also, women with HNPCC have a 30-50% lifetime risk of endometrial cancer. The average age of diagnosis of endometrial cancer is about 46 years. Among women with HNPCC who have both colon and endometrial cancer, about half present first with endometrial cancer. In HNPCC, the mean age of diagnosis of gastric cancer is 56 years of age with intestinal-type adenocarcinoma being the most commonly reported pathology. HNPCC-associated ovarian cancers have an average age of diagnosis of 42.5 years-old; approximately 30% are diagnosed before age 40 years. Other HNPCC-related cancers have been reported with specific features: the urinary tract cancers are transitional carcinoma of the ureter and renal pelvis; small bowel cancers occur most commonly in the duodenum and jejunum; the central nervous system tumor most often seen is glioblastoma.
Familial Gastrointestinal Cancer Registry - A family study centre at Mount Sinai Hospital, Toronto, for rare inherited colorectal cancer syndromes, including familial adenomatous polyposis (FAP), hereditary nonpolyposis colorectal cancer (HNPCC), Peutz-Jeghers syndrome, juvenile polyposis, and other polyposis syndromes.