When there are multiple cases of colorectal cancer in one family, it may be due to chance, shared environmental factors, known or unknown genes, or a combination of genes and environment. Approximately 5 to 10 percent of colorectal cancers are hereditary, where the risk is passed in specific versions of genes, from parent to child. You should let your doctor know if you have a family member who was diagnosed with colorectal cancer, especially if it was a first-degree relative (brother, sister, or parent). You may need to begin colorectal cancer screening at age 40 or earlier, depending on the age that your family members were diagnosed with colorectal cancer.

Hereditary cancer syndromes

There are also several hereditary cancer syndromes that increase your risk of colorectal cancer and other cancer types. Below are some of the common hereditary cancer syndromes that increase colorectal cancer risk.

  • Lynch syndrome: Also called hereditary nonpolyposis colorectal cancer (HNPCC), this inherited disorder increases the risk of several cancers, including colon, uterine, ovarian, stomach, small intestine, urinary tract/bladder/kidney, bile duct, pancreas, sebaceous gland, and brain (usually glioblastoma) cancer.
  • Familial adenomatous polyposis (FAP): Patients with FAP develop hundreds to thousands of precancerous growths in the colon, called adenomatous polyps. Individuals with FAP have an increased risk for other cancers, including stomach, small bowel, pancreas and bile duct, liver, thyroid, and central nervous system (usually medulloblastoma). Some people with FAP have stomach polyps, small bowel polyps, and other types of benign growths and tumors.
  • MUTYH associated polyposis (MAP): Patients with MAP develop growths in the colon, called adenomatous polyps (usually 20 to 100). Those with MAP may also develop colon cancer without polyps. Unlike most of the genetic conditions that we know increase cancer risk, MAP is recessive in inheritance. This means that individuals with this condition may be the first member of the family to be affected if two parents that do not have the disease pass one copy of the non-working MUTYH gene to their affected child.
  • Many other genes are known to increase the risk for colon polyps, colorectal cancer and other cancers. A genetic counselor helps to ensure that the appropriate tests are made available to you and your family.

Visit our UCLA Cancer Genetics to learn more about when genetic counseling and genetic testing are recommended.