Bowel cancer – symptoms, referrals, and early detection

  • 26 June 2021
  • Dr Jane Strang

For Bowel Cancer Awareness month, we asked Nelson-based general surgeon Dr Jane Strang to write an opinion piece about the symptoms, what to include in your referral, the benefits of bowel screening, and early detection. 

Bowel cancer is the most commonly reported cancer in New Zealand, with approximately 3,100 cases and 1,200 deaths per year. Bowel cancer has the second highest rate of cancer-related death in New Zealand, but it can be treated successfully if it is detected and treated early.

Symptoms of bowel cancer include...

  • A sustained change in bowel habits - In particular, diarrhea that has been going on longer than six weeks, and infectious causes have been excluded. Constipation alone is rarely the presenting complaint of bowel cancer and a trial of dietary modification, a fibre supplement (the best one out there is Benefibre, unfortunately not available on prescription but found at supermarkets or pharmacies) and encouraging exercise should be recommended to the patient unless they have any other alarming symptoms.
  • Feeling of incomplete rectal emptying
  • PR bleeding - Often the blood is altered in colour (often plum colour but can be black if from the right colon) but fresh bleeding from a low rectal cancer can easily be passed off with “it’s just hemorrhoids.” Don’t forget to get a digital rectal examination, and if you can feel a lump in the rectum, it’s not hemorrhoids. Hemorrhoids cannot be felt as they are a distended vein that once digital pressure is applied will collapse. 
  • Abdominal pain - this is a relatively rare presentation of bowel cancer unless the cancer is causing a stenosis with bowel obstruction or it is locally invading the abdominal wall.

Risk factors...

Patients are more at risk of bowel cancer if:

  • There is a history of family members over two or three generations being affected by bowel cancer
  • A close family member has been diagnosed with bowel cancer under the age of 55 years
  • There is a known genetic bowel cancer syndrome in the patient’s family
  • The patient has a history of extensive inflammatory bowel disease such as ulcerative colitis for more than ten years

What to include in your referral... 

When referring to a public hospital to request a colonoscopy, you will need to include the following:  


  • duration of symptoms
  • information on rectal bleeding
  • change in bowel habit with Bristol stool chart
  • personal history of adenoma
  • personal history of CRC
  • family history of CRC
  • previous colonoscopy (if the patient has previously had a colonoscopy for exactly the same symptoms they are seeing you for. Another colonoscopy is unlikely to show any new pathology)
  • ability for the patient to tolerate bowel preparation.


  • abdominal masses
  • PR examination findings


iron-deficiency anemia

Procedure risk

anti-coagulation/anti-platelet medication - what and why?

Medical history 

  • past medical history
  • medications
  • allergies

Early detection and bowel screening 

We use bowel screening to detect pre-cancerous polyps, which can be removed at the colonoscopy, or early cancers. People who are diagnosed and receive treatment at an early stage have a 90% chance of long-term survival.

While bowel screening is available for patients aged 60-74 years, the average age of patients who get bowel cancer is 65 – which is why I would like to see the eligible age for screening come down to at least 55, and 50 for Māori. The common types of polyps take 7-10 years to become malignant. 

Screening involves the patient using an at-home fecal immunochemical (FIT) test sent by the bowel screening programme. The FIT test detects small traces of blood present in bowel motion. Just because someone has a positive FIT test does not mean there will be anything nasty to find, about 7 in 10 people will have polyps which can be removed at the time of the colonoscopy, and about 7 in 100 will be found to have cancer and require treatment.

Treatment of bowel cancer usually means the patients will go on to have an operation unless they have too many co-morbidities, or they don’t want to. Sometimes the cancer has spread so far that the patient will not benefit from surgery and if they can tolerate it, chemotherapy would be offered, or they may need to go to palliative care.

Prior to surgery we will do a CT scan, carcinoembryonic antigen test (CEA) and, if a rectal cancer is found, an MRI scan of the pelvis. (Rectal and colon cancers are very different beasts to treat). The CEA is used to follow patients up after treatment, it is not a diagnostic test, so please don’t do a CEA for any patient unless they have a known bowel cancer. 

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