There are approximately 30,000 cases per year and 15,000 deaths per year in the UK. This disease occurs more commonly in males than in females, with an age-standardised male:female ratio of 1.5:1. There is a transition from colonic mucosa tissue to adenoma (dysplastic or villous) formation and then to carcinoma, which involves a sequence of alterations in specific genes.6
The majority of bowel cancers are sporadic, caused by an interaction between lifestyle, environment and genetics. They commonly occur between 60 and 70 years of age, usually in the rectum and sigmoid colon. As many as 20% of patients who are affected by bowel cancer may have a family history. Around 10% of colorectal cancers may be caused by a genetic susceptibility. In particular, the Ashkenazi Jewish population has an increased risk of developing bowel cancer, and 5% of this population may carry an altered APC gene, which predisposes to colorectal cancer.
Familial adenomatous polyposis (FAP)
This condition arises from germ-line alterations in the APC gene on chromosome 5q21-22, and accounts for 1% of patients affected with colorectal cancer. Affected cases may develop hundreds of adenomas by the second to third decade of life, which invariably give rise to colorectal cancer if prophylactic colectomy is not performed. This is performed early, and is followed by annual sigmoidoscopy of the residual rectal area. There are extracolonic associations, which include gastric cancers and osteomas. There are also attenuated forms of FAP.