Most cases of cancer in the colon and rectum develop sporadically, which means that there is no known hereditary (genetical) disposition for the cancer development. 20 -30% of the cases may have a hereditary disposition as there is enhanced incidence in families or the cancer appears at young age. A specific genetic cause is known in less than 5% of the cases.
In about 95% of all cancer in the colon/rectum there is no known cause. The risk for developing this type of cancer increases with age.
- Lynch syndrome, HNPCC (hereditary, non-polypous colorectal cancer is found in around 2-4% of all cancer in the colon/rectum. This genetic aberration is identified and may be tested in the patient and in uninvolved family members. The life-time risk for developing cancer in a person with Lynch syndrome is 60-80%. This genetic aberration increases the risk for developing cancer in the uterus (the endometrium) and ovaries, the pancreas, stomach, small intestine and kidneys.
- Familial adenomatous polypous (FAP) constitute around 1% of cancer in the colon/rectum. Nearly all with this condition will develop cancer, mostly before 30 years of age.
- Around 15-25% of the cancers appear in families with an enhanced incidence of colorectal cancer, without known genetic aberrations.
These cancers primarily develops as polyps. The majority of polyps will disappear spontaneously but around 10% will develop into cancer, usually within 8-10 years. The polyps which develop into cancer are either adenomas or a special kind of hyperplastic polyps called serrated adenomas. Ordinary hyperplastic polyps do not develop into cancer.
- Environment and life-style - High fat intake, fried foods, frequent use of tobacco and alcohol, obesity and inactivity are probably associated with increased incidence of colorectal cancer.
- Inflammatory bowel disease (ulcerative colitis/Chrohn’s disease) increases the risk of colorectal cancer.
- Previous irradiation.