Bowel Cancer

Incidence

Since 1975, there has been a rapid increase in the incidence of bowel cancer in Australia, which appears to be related to Western lifestyle, although “lifestyle” may encomapss many factors, as yet uncertain but probably resulting in genetic changes.  Australia, together with New Zealand, the United Kingdom and the United States of America have some of the highest incidences of bowel cancer in the world.  Migrants to Australia from low risk countries begin to show an increased risk of bowel cancer within ten years of arrival, and migrant communities will have reached the general Australian risk within two generations.

Bowel cancer is seen most commonly in people between the ages of 50 and 80, but 10% of cases are now known to occur in those under 50 years of age.

Although some are at higher risk (in particular, those with a strong family history of bowel cancer), 85% of patients presenting with bowel cancer will have no identifiable risk factors.

Symptoms

The most common symptoms of bowel cancer are:

• rectal bleeding;
• blood or mucus in the faeces (bowel motion);
• an unexpected change in bowel habit (ie, diarrhoea or constipation);
• lower abdominal pain or swelling;
• tiredness;
• weakness;
• a feeling of incomplete emptying of the bowel; and
• weight loss without an obvious reason.

Surgical cure rates

There have been significant advances in the treatment of established bowel cancer in the last 30 years.  These gains, have been the result of using newer techniques to avoid the necessity for permanent stomas and by the development of specialised training programmes in colorectal surgery, used in combination with sophisticated radiotherapy and chemotherapy treatment schedules.

Overall we cure 50% of bowel cancers that present with symptoms, but that proportion is higher in patients whose cancers are diagnosed as part of a screening program and therefore at an earlier stage.  The improving rate of cure for bowel cancer in NSW is now up to 60%, thus seems to be due to earlier diagnosis.  In turn, earlier diagnosis may in part to be due to somewhat better community awareness of the need to investigate bowel symptoms.

Screening for polyps

In addition to early diagnosis of bowel cancer, screening programs can prevent the disease.  Nearly all bowel cancers start as polyps, small “warty” growths that appear on the surface of the bowel lining.  Polyps are very common, especially as people become older, most developing during and beyond the fifth decade of life.  Most polyps do not become cancerous; but almost all cancers arise from a polyp.  Note, with breast and prostate cancer screening, a positive test indicates cancer (albeit early in development and thus potentially curable), whereas the identification and removal of colonic polyps will actually prevent cancer.  Indeed, it takes probably between 5 and 15 years for a polyp to become cancer.

Types of screening

Broadly speaking, there are currently four methods of screening available:

• testing for unsuspected blood loss in the bowel, called faecal occult blood testing (FOBT);
• radiological techniques;
• computerised tomographic colonography (or “virtual” colonoscopy) and
• colonoscopy.

See Detecting Bowel Cancer below.

Future Issues

Among the issues related to screening which require clarification are:

• age of commencement of screening;
• appropriate screening intervals;
• cost-effectiveness of various modalities in the Australian setting;
• the most effective methods of combining the screening modalities; and
• a clear definition of the utility of various tests in people of differing risk profiles.

These issues require definition, not only because of the obvious benefits to the community from effective prevention and early diagnosis of bowel cancer, but also because of the overall cost of such screening to the community.  For example, lifetime screening applied now for all Australians between the ages of 50 and 69 years, using the cheapest test (FOBT) carried out every two years, together with follow-up colonoscopy of all those with positive results, has been recommended as optimal cost-effective care at this time.  It is clearly important that efforts be made to answer the questions posed above and epidemiological research be undertaken to answer these questions should be of high priority.

Lifestyle

You can reduce your risk of bowel cancer by:

• maintaining a healthy weight;
• ceasing smoking;
• regularly exercising;
• maintaining a healthy diet that is high in fibre;
• eating plenty of fruit and vegetables, and a small amount of meat;
• undergoing regular screening for polyps from the age of 50 years; and
• having any and all polyps investigated.