What is bowel cancer?

Bowel cancer (also called colorectal cancer) is a disease caused when cells in the lining of the large intestine (colon and rectum) grow out of control and form a lump. Most cancers start as small harmless polyps, which then grow bigger and eventually turn malignant. Cancers tend to grow quite slowly over many months or even years, so often go unnoticed for a long time.

A cancer can cause a problem where it is locally, or it can spread to other parts of the body. The tumour in the bowel is likely to bleed and can narrow it, eventually causing a blockage (obstruction). Cancer cells shed by the primary tumour can spread to the glands (lymph nodes) near the bowel, or they can get into the bloodstream and travel to other regions: the liver and lung are most commonly affected.


Some early cancers may give no symptoms at all and even when the cancer has spread the secondary deposits often do not cause any noticeable effects. For this reason screening for cancer is very worthwhile to detect cancers at an early stage or even prevent them from forming.

Here are some common symptoms of cancer – but please note that almost all of these symptoms can be caused by other conditions such as haemorrhoids or inflammation of the bowel. That is why if you have symptoms, you need to have them assessed and then tests arranged to find out what is causing them, principally a telescope examination of the bowel, a colonoscopy.

  • Bleeding - this is noticeable on the toilet if there is blood on the paper or dripping into the toilet, or if there is blood mixed into the stool. Cancers tend to bleed darker blood than for example haemorrhoids which typically bleed bright red.
  • Altered bowel habit - typically a bowel cancer will result in a looser stool and more frequent bowel action than usual. Constipation is not a common bowel cancer symptom. Similarly, bowel symptoms which are intermittent, with periods of completely normal function, tend not to be due to a cancer. Any persistent change in the bowels should be investigated however.
  • Incomplete evacuation – if there is a tumour in the rectum its presence may be misinterpreted by the body as some stool that has not been passed. The medical word for this is ‘tenesmus’.
  • Anaemia – strictly speaking anaemia is not a symptom, but may come to light when tiredness or undue breathlessness are investigated. Anaemia can develop even when there is no overt bleeding from the bowel and is a common way in which tumours of the first part of the colon, the caecum, are discovered.
  • Obstruction – a bowel obstruction is fortunately rare but can be the first sign of a cancer


Once the suspicion has been raised that there might be a problem the first simple diagnostic test is a finger examination of the rectum – many rectal cancers can be felt as they can be close to the anus. Further investigations are listed below:

  • Rigid sigmoidoscopy – this is a simple examination of the back passage with a small tube and has the advantage that it can be performed in the clinic. In addition samples (biopsies) can be taken painlessly to make a diagnosis.
  • Colonoscopy - this is the gold standard method of examining the whole bowel. It involves passing a thin steerable tube into the rectum through the anus and guiding it through the whole colon to reach the caecum and appendix area. It is commonly performed under light sedation as a day-case procedure.
  • CT scan – an X-ray examination of the whole body can reveal the primary tumour itself and will show up secondary deposits, for example, in the liver or lungs.
  • MRI scan – this is particularly useful at getting more information about a rectal cancer and any lymph node spread within the pelvis to help to determine what the best combination of treatments should be.


The treatment of bowel cancer very much depends on the stage of the disease – ie how advanced it is. If there is no obvious spread outside the bowel then surgery is the mainstay of treatment with a view to cure. Surgery will generally involve removing a section of the bowel along with the adjacent lymph nodes (a colectomy) and then joining up the bowel again (anastomosis). Often operations for bowel cancer can be performed by "keyhole" (laparoscopic) surgery. Chemotherapy is often recommended after surgery to improve the likelihood of cure.

Cancers involving the rectum are more complicated than those of the colon; often a combination of radiotherapy, chemotherapy and surgery are appropriate and your Consultant will discuss this in detail as each person’s treatment is tailored to the individual circumstances.

The Consultants in the Cambridge Bowel Clinic work in a large multidisciplinary team, an MDT. This group includes the surgeons, oncologists, radiologists, histopathologists and specialist nurses. All patients with bowel cancer are discussed at a weekly meeting at Addenbrooke’s to enable the most appropriate and up to date treatment to be provided to each patient at a consistently high standard.