General Practice

Colorectal cancer | Family history is an important indicator

Knowing your detailed family medical history is an incredibly important part of doctors being able to identify your inherited cancer risk. As many as 1 in 3 people who develop colorectal cancer have other family members who have had it.

What is colorectal cancer?

Colorectal or bowel cancer is a cancer that affects the digestive system between the stomach and the anus. It can affect either the small bowel where our food is digested, or the large bowel (colon and rectum) where what remains of our food is turned into solid waste and expelled from the body. This page deals primarily with cancer of the large bowel (also known as colon or colorectal cancer) which is more common than small bowel cancer.

Characteristic symptoms of colorectal cancer include changes in bowel habits and bleeding from the rectum. Treatment involves surgery, followed in some cases by chemotherapy or radiation therapy. In many cases, colorectal cancer is curable if detected sufficiently early in the course of the disease.

About bowel and colorectal cancer

Bowel cancer, along with prostate cancer, is one of the most diagnosed cancers among New Zealand adults with around 3000 new cases per year.  New Zealand has one of the highest rates of bowel cancer and deaths from bowel cancer in the western world.


It is not known what causes bowel / colorectal cancer, but several risk factors that appear to increase the likelihood of developing the disease have been identified.

A family history of bowel cancer or polyps – having a first-degree relative (father, mother, brother, sister) or second-degree (grandfather, grandmother, aunt, uncle) relative with bowel cancer or polyps – is a risk factor for bowel cancer.

The risk of developing the condition is also increased in people with an inflammatory bowel disease, primarily long term ulcerative colitis but also some instances of Crohn’s disease.

Diets high in fat are believed to be a factor in the development of bowel cancer – countries with high rates of bowel cancer have a higher consumption of fat than countries with low bowel cancer rates. It is thought that digestion of fat in the colon results in the formation of cancer-causing chemicals (carcinogens). Consuming less fat should help to reduce exposure to these fat-derived carcinogens.

Signs and symptoms

Signs and symptoms of colorectal cancer are many and varied, including:

  • Blood in the stools and/or bleeding from the rectum
  • A change in bowel habit lasting longer than 6 weeks (e.g. loose stools, diarrhoea or constipation)
  • Stomach pain (often severe)
  • Lumps or a mass in the abdomen
  • Weight loss

Weakness and tiredness (symptoms of anaemia).

If you feel like this may be relevant to you, please do not hesitate in seeing your GP.