Family risk of bowel cancer

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There are numerous reasons why some people get cancer and others do not despite leading similar lifestyles. In general, there is a lower risk of bowel cancer, and all cancers, in populations who eat more fresh fruit and vegetables, exercise regularly, avoid excessive meat intake, dietary chemical, smoking, industrial chemicals and radiation. Nevertheless many people with this lifestyle may develop cancer, probably due to a vulnerability in their genetic makeup.

There is always an increased likelihood of developing bowel cancer in people whose close relatives had the diagnosis of this condition. Having a first degree relative with bowel cancer (mother, father, sister, brother or child) considerably increases the risk of getting bowel cancer. The more relatives with the condition, the higher the risk. In a very small percentage of cases the risk is very high and directly inherited from parent to child – these are people with genetic bowel cancer syndromes. People with strong family history of colorectal cancer should start testing and screening for bowel cancer well before the age of 50. It is worth noting though, that in about 80 per cent of cases there is no history of bowel cancer in the family.

 There are two major forms of family bowel cancer disposition:

• The first is familial adenomatous polyposis (FAP). People with this condition have polyps growing in the wall of the bowel which can become cancerous if these are not removed. Polyps are small benign (non-cancerous) growths which occur very commonly in the large bowel. Most bowel cancers start in a polyp (though most polyps do not become cancerous - only about 5% do). 
• The second condition which may run in the family is called hereditary non-polyposis colorectal cancer (HNPCC). This condition is connected with mutation in certain genes.

What causes cancer: Within each cell, in the human body, lies strips of  DNA containing millions of genes. Some of these genes cause cancer but are kept from mischief by other genes which lie next to them on the same strip of DNA. These good genes, called tumour suppresser genes, guard the body from the bad cancer genes. Essentially we were born with the tendency to get cancer. How well our good genes (tumour suppressor genes) lock our bad genes depends on our individual genetic makeup (the cards we were dealt). Certain factors in our environment can damage our DNA and split the suppressor genes from the cancer genes allowing cancer to develop. For bowel cancer these consist of:

Personal and/or family history: people with a personal history of colorectal polyps or cancer are at greater risk of getting bowel cancer. A personal history of chronic inflammatory bowel disease (IBD) sometimes leads to malignancy as well. Irritable bowel syndrome (IBS) is a different condition which does not carry an increased risk of bowel cancer. Some people were born with an increased genetic susceptibility to bowel cancer or inherited this genetic disposition from their family members. There is always an increased likelihood of developing a cancer if it "runs" in the family - especially if the first degree relatives (parent, brother or sister, child) became ill before the age of 60. People with strong family history of colorectal cancer should start testing and screening for bowel cancer well before the age of 50.

Causes

But first a brief explanation of how the bowel works. After leaving the stomach, food passes into the small intestine where the food is broken down and nutrients absorbed (cancer, incidentally, is very rare in the small intestine). The remnants then pass into the large intestine, the (approximately) one-metre muscular tube made up of the colon and the rectum. As the remnants of digestion pass along, water is absorbed until they pass into the rectum and are expelled through the anus as faeces.

Cancer can occur at any part of the colon or rectum. When it occurs in the colon bowel cancer is also known as colon cancer; when it's in the rectum, it's called rectal cancer. Bowel cancer is sometimes also called colorectal cancer, a term which covers both colon and rectal cancer.

Colorectal cancer is caused by a mutation in the cells of the lining of the bowel. The cells are gland cells, so the cancer is of a type called adenocarcinoma. What triggers these changes isn't known. But it's more likely in people with certain risk factors:

• Age. Colorectal cancer is more common in older people. It's rare under the age of forty, but after this, the risk increases as a person gets older.
• Family risk. It's more likely if someone in the family has it. Having a first degree relative with it – for example a mother, father, sister, brother or child – increases the risk of getting bowel cancer by a factor of three. The more relatives with the condition, the higher the risk. In a very small percentage of cases the risk is very high and directly inherited from parent to child – these are people with genetic bowel cancer syndromes. It's worth noting though, that in about 80 per cent of cases there's no history of bowel cancer in the family.
• Low-fibre diet. Bowel cancer is probably more common in people who don't have much fibre in their diet and who eat a lot of red meat and fat. In societies that have a lot of fibre in the diet – vegetables and grains for example (as in Africa and Asia) – bowel cancer is much less common compared to those societies which consume plenty of red meat and fat, but not much fibre (like Australia and the US).
• Polyps. A polyp is a small benign (non-cancerous) growth that looks roughly like a ball on a stalk. Polyps occur in many of the body's internal cavities and surfaces, and they're very common in the large bowel – about one person in four over the age of 50 has them. Most bowel cancers start off in a polyp (though most bowel polyps don't become cancerous – less than 5 per cent do). In other words, someone with polyps in the colon has an increased risk of getting bowel cancer. In some rare hereditary conditions the tendency to develop bowel polyps is passed from parent to child, and these people are at particular risk of bowel cancer. There are two of these conditions; hereditary non-polyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP).
• Colitis. People with inflammatory bowel conditions such as ulcerative colitis and Crohn's disease are at increased risk of bowel cancer.

Further general information Your doctors and specialist nurses are in an ideal position to give you relevant information on your disease and treatment as they know your individual circumstances. Cancerbackup has a help line (0808 800 1234) and a prize winning video available in English, Italian, Urdu, Bengali, Gujarati & Hindi explaining Radiotherapy & Chemotherapy. Cancernet.co.uk has over 500 pages describing cancer, its management, practical tips and tool which patients, their carers and their doctors have found helpful during the cancer journey.