Bowel (colorectal) cancer

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What is bowel (colorectal) cancer?

Bowel cancer is when normal cells in your bowel change and grow in an abnormal way. A group of these cancer cells can form a tumour. Bowel cancer is a common cancer in Ireland. About 2,500 people are diagnosed with it each year.* 

Cancer that begins in the large bowel is called colon cancer. This cancer may cause a blockage in your bowel, which can affect how your bowel works. Cancer of the rectum occurs very low down in your bowel close to your anus.

What is the bowel and what does it do?

The bowel is part of your digestive system. It is made up of the small bowel and the large bowel. 

The large bowel contains your colon and rectum. Most cancers occur in the large bowel.

When you swallow food, it goes from the gullet (oesophagus) to your stomach and into your small bowel. Food is digested in the small bowel and nutrients are taken into the body. In the large bowel, water is absorbed from digested food.

The waste matter that is left (called faeces, stool or poo) is stored in the rectum (back passage) until ready to pass out of the body through the anus - the opening to the outside of your body. 

Medical content updated from our 'Understanding bowel (colorectal) and anal cancer' booklet (2022), reviewed by Mr Saqib Zeeshan, Consultant General & Colorectal Surgeon, Mary Sweeney, Colorectal Nurse Specialist and Teraze Toby, Daffodil Centre Nurse.

*The Irish Cancer Society uses the most up-to-date cancer statistics from the National Cancer Registry Ireland, available on www.ncri.ie