Colorectal Cancer

Other names: bowel cancer, cancer of the colon and rectum

Colorectal (colon and rectum) cancer is the most common internal cancer in Australia. There are about 40 new patients per 100,000 of the population diagnosed each year (approximately 7000 for the whole country). The incidence (number of new patients diagnosed each year) is slowly increasing but this is mainly because of an increase in colorectal cancer in elderly people. In younger people (< 45 years) the incidence is actually decreasing, possibly due to improvements in diet and lifestyle.

Colorectal cancers arise from colorectal adenomas (a particular type of benign polyp). Polyps are common (see Colorectal Polyps) and only a small proportion of colorectal polyps turn into cancers; this process takes many years. The cause of colorectal cancer is not completely understood although a western diet (particularly one that is high in red meat and fatty foods, and low in vegetables, fruit and cereals) may increase the risk of colorectal cancer, although the precise reason is not known. Genetic factors are also very important, as discussed below.

Frequency in the Community

About 25-30% of patients with colorectal cancer have a 'risk factor'. Some of the risk factors are: family history of colorectal cancer or adenomas in first degree relatives (ie. parents, brothers and sisters, or offspring); hereditary non-polyposis colorectal cancer (HNPCC or Lynch syndrome); inherited polyposis syndromes such as Familial Adenomatous Polyposis (FAP); previous colorectal cancer; chronic ulcerative colitis and possibly Crohn's disease.

There is good evidence that a family history of colorectal cancer or adenomas in first degree relatives (ie. parents, brothers and sisters, or offspring) is associated with an increased risk of colorectal cancer and adenomas in other family members. It is therefore recommended that first degree relatives of a patient with colorectal cancer have a colonoscopy commencing between age 40 and 50, or at an age that is 5-10 years younger than the youngest relative with colorectal cancer. There are also a number of important genetic syndromes associated with a high risk of colorectal cancer, hereditary non-polyposis colorectal cancer (HNPCC or Lynch syndrome) and inherited polyposis syndromes such as Familial Adenomatous Polyposis (FAP).


The symptoms of colorectal cancer are very similar to the symptoms of many other bowel diseases: change in bowel habit; bleeding or passage of mucus from the bowel; abdominal pain or discomfort; constipation; diarrhoea, and weight loss. Some patients have no symptoms or present with iron deficiency anaemia. The symptoms are often quite minor.


The diagnosis of colorectal cancer is usually made by examination of the colon (colonoscopy, flexible sigmoidoscopy, barium enema x-ray, or CT colonography). Colonoscopy is preferable since this allows a complete examination of the colon and biopsy of any abnormality for examination by a pathologist. A full colonoscopy may not be possible (for instance, if the bowel is obstructed) and the diagnosis may be made by other means.


The main treatment of colorectal cancer is surgical, ie. removal of the tumour and the nearby lymph glands. The disease is staged: Dukes A, cancer limited to the bowel wall; Dukes B, extending through the wall; Dukes C, involving the lymph glands; Dukes D, spread beyond the bowel and the lymph glands. There are other, more sophisticated, staging systems. In some patients (particularly Dukes stage C) chemotherapy may be useful to reduce the chance of the cancer coming back. In patients with cancer of the rectum (lower bowel) surgery, chemotherapy, and radiotherapy all have an important role in treatment, depending on the stage of the disease and the patient's age and fitness.

While more than half of all patients diagnosed with colon cancer will be cured, some will not be cured. Although there have been improvements in surgical technique and other treatments for patients with colorectal cancer, it seems likely that the best results will come from either prevention of colorectal cancer, or early detection long before symptoms occur. Faecal occult blood testing (detection of minute amounts of blood in the faeces) is one technique which is currently being used for population screening.