Lynch syndrome

Lynch syndrome, often called hereditary nonpolyposis colorectal cancer (HNPCC), is a type of inherited cancer of the digestive tract, particularly the colon (large intestine) and rectum. People with Lynch syndrome 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 high risk of cancer of the endometrium (lining of the uterus) and ovaries. Even though the disorder was originally described as not involving noncancerous (benign) growths (polyps) in the colon, people with Lynch syndrome may occasionally have colon polyps. In individuals with this disorder, colon polyps occur at an earlier age than in the general population. Although the polyps do not occur in greater numbers than in the general population, they are more likely to become cancerous.

In the United States, about 160,000 new cases of colorectal cancer are diagnosed each year. Approximately 2 percent to 7 percent of these cancers are caused by Lynch syndrome.

Variations in the MLH1, MSH2, MSH6, and PMS2 genes increase the risk of developing Lynch syndrome. 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.

Read more about the MLH1, MSH2, MSH6, and PMS2 genes.

Lynch syndrome cancer risk is inherited in an autosomal dominant pattern, which means one inherited copy of the altered gene in each cell 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.