Bowel cancer, also known as colorectal cancer, means cancer that starts in the colon (large bowel) or back passage (rectum).
It is the 4th most common cancer in the UK, with around 41,000 people diagnosed in the UK each year. Both men and women can get bowel cancer: most are aged 50 or over when they are diagnosed.
The risk of developing bowel cancer depends on many factors, including:
- genetics and family history
- medical conditions such as
- familial adenomatous polyposis (FAP) (a rare inherited condition responsible for less than 1% of cases)
- Lynch syndrome (people with this gene fault have a higher risk of getting bowel cancer and other cancers)
- Ulcerative Colitis and Crohn’s Disease (see section below on Inflammatory Bowel Disease)
- diet and lifestyle factors
- radiation (a small number of cases are linked to radiation exposure from radiotherapy treatment for previous cancer, radiation used in tests such as x-rays and CT scans (diagnostic radiation) or background radiation).
How bowel cancer grows and bowel adenomas
The bowel walls are made up of several layers of body tissues. Bowel cancers start in the innermost layer – the lining. Most begin as a small growth called a polyp or adenoma. If left untreated, they might become cancerous and grow into the muscle layers under the lining of the bowel and then through the bowel wall.
The cancer can then spread into organs that are close to the bowel, such as the bladder, womb or prostate gland.
Doctors think most bowel cancers take 5 to 10 years or more to develop.