Bowel cancer is also known as colon, rectal, or colorectal cancer. The lining of the bowel is made of cells that are constantly being renewed. Sometimes these cells grow too quickly, forming a clump of cells known as a bowel polyp (sometimes called an adenoma). Polyps are not bowel cancers (they are usually benign), but they can change into a malignant cancer over a number of years. A malignant cancer is when cancer cells have the ability to spread beyond the original site and into other parts of the body. When the cancer first starts to develop, there are typically no symptoms for several weeks or months, and in some cases even longer. Then, as the cancer progresses, the common initial symptoms include bleeding from the rectum (back passage), change in your bowel habits (for example, having prolonged episodes of diarrhoea), and anaemia, which can lead to tiredness.

Both men and women are at risk of developing bowel cancer. In the European Union, bowel cancer is the third most common cancer and the second leading cause of death due to cancer, with more than 345,000 new cases and 150,000 deaths estimated in 2012. About 1 out of 20 people in the European Union will develop bowel cancer during their lifetime. About 8 out of 10 people who are diagnosed with bowel cancer are older than 60 years. About 5 out of 10 people diagnosed with bowel cancer will die of the disease; the risk of dying is lower if a cancer is detected at screening.