Colon cancer, family history of: The presence of a history of colorectal cancer in a family. The colon cancer risk is higher if an immediate (first-degree) family member (parents, siblings or children) had colorectal cancer and even higher if more than one such relative had colorectal cancer or if a family member developed the cancer at young age (younger than 55 years). Under any of these circumstances, individuals are recommended to undergo a colonoscopy every three years starting at an age that is 7-10 years younger than when the youngest family member with the cancer was diagnosed. For example, if a parent had colon cancer diagnosed at age 50, colonoscopy should start in that person's children at 40-43 years of age.

See: Colon cancer family history.