What is bowel cancer?

Bowel cancer is cancer that starts in the large bowel (colon) or back passage (rectum). It is also known as colorectal cancer.

Cancer is when abnormal cells start to divide and grow in an uncontrolled way. The cells can grow into surrounding tissues or organs, and may spread to other areas of the body. 

The bowel makes up a part of the digestive system. It’s split into the small and large bowel. The large bowel includes the:

  • colon
  • back passage (rectum)
  • bowel opening (anus)

This section is about colon and rectal cancer. We have separate sections about anal cancer and small bowel cancer.

Where does bowel cancer start?

Where your bowel cancer starts will affect the treatment that you might have. For example, the treatment for colon cancer can be different to the treatment for rectal cancer.

Colon cancer

The colon is the first part of the large bowel. It is about 5 feet long and has 4 sections. Cancer can develop in any of these. 

The parts of the colon are the:

  • Ascending colon – runs up the right side of the abdomen. It is connected to the small intestine by a section of bowel called the caecum
  • Transverse colon – runs across the body from right to left, under the stomach
  • Descending colon – runs down the left side of the abdomen
  • Sigmoid colon – an 'S' shaped bend that joins the descending colon to the back passage
Diagram showing the parts of the large bowel

Rectal cancer

Rectal cancer starts in the last part of the large bowel (the back passage). This part of the bowel stores poo (stool) until it is ready to be passed out of the body. 

Rectal cancer is also called cancer of the rectum.

Anal cancer

Anal cancer starts in your anus which is the opening at the very end of your large bowel. Poo leaves your body through your anus. 

Cancer of the small bowel

The small bowel is between the tummy (stomach) and large bowel.

If bowel cancer spreads

Bowel cancer can spread to another part of the body through the lymphatic system. The lymphatic system is made up of lymph nodes, which are part of the body’s immune system. One of the first places bowel cancer spreads is to the lymph nodes in the tummy (abdomen).

Bowel cancer can also spread to other parts of the body through the bloodstream. The liver is a common place for colorectal cancer to spread because blood flows directly from the bowel to the liver. The cancer can also spread into the lung or bone but this is less common.

Diagram showing the most common sites for bowel cancer to spread to

How common it is

Around 42,300 people are diagnosed with bowel cancer in the UK each year. It is the 4th most common cancer in the UK.

Who gets it

Both men and women can get bowel cancer. It is more common in older people.

The risk of developing bowel cancer depends on many factors, including:

  • age
  • genetics and family history
  • medical conditions such as familial adenomatous polyposis (FAP), Lynch syndrome, ulcerative colitis and Crohn’s disease
  • diet and lifestyle factors
  • radiation
Last reviewed: 
27 Jul 2018
  • Cancer Incidence from Cancer Intelligence Statistical Information Team at Cancer Research UK  (2015 - 2017 UK average) 
    Accessed September 2020

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  • Rectal cancer: ESMO clinical practical guidelines for diagnosis, treatment and follow up
    R Glynne-Jones and others
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