Approximately
10 per cent of Colon cancers have a strong genetic factor. The
commonest is hereditary non-polyposis colon cancer (HNPCC or Lynch
syndrome). This condition is caused by mutation in any one of at least
five different genes.
The best available approaches for a low risk of developing Colon cancer are:
- a diet high in green vegetables, particularly cabbage, broccoli, brussel sprouts or cauliflower.
- a diet low in red meat. In particular, avoid burnt meat, which contains cancer-promoting chemicals called cyclic amines.
- keeping to a normal body weight and taking regular exercise.
- Although still controversial, it seems that taking aspirin (eg Disprin)
regularly (300mg per day or more ie one standard tablet) reduces the
risk by about 50 per cent. However, prolonged use of aspirin carries a
risk of intestinal ulceration and bleeding, so whether the benefits
would outweigh the risks is unclear at present.
Genetic factors
Approximately 10 per cent of Colon cancers have a strong genetic
factor. The commonest is hereditary non-polyposis colon cancer (HNPCC
or Lynch syndrome). This condition is caused by mutation in any one of
at least five different genes. These genes carry the instructions for
manufacturing proteins that can repair damaged DNA.
Inheritance of this type of cancer is autosomal dominant, which means
that half the children of someone with HNPCC are at risk of inheriting
the condition. When these genes are defective, DNA repair does not take
place, and damaged (mutant) DNA accumulates within cells, greatly
increasing the cancer risk.
The colon is not the only organ affected. The syndrome also carries an
increased risk of cancers of the stomach, ovaries, breasts and uterus.
The Colon cancers in affected individuals tend to develop as flat
lesions rather than as polyps. The cancers more commonly affect the
proximal (right sided) colon, whereas other cancers are more common in
the distal colon (nearer the rectum) or rectum. They occur at a younger
age and this condition should be suspected in anyone who develops Colon
cancer before the age of 45.
About 1 per cent of Colon cancers occur in people who inherit a defect
in the gene for familial polyposis coli. These people develop hundreds
of adenomatous (pre-cancerous) polyps in the colon by the time they are
in their teens and almost invariably develop Colon Cancer by middle age unless the colon is removed.
Patients with ulcerative colitis or Crohn's disease of the colon
(conditions that together affect about 1 in 800 of the population in
Western countries) have about a five-fold increased risk of Colon
cancer.
The risk is greater if the colitis (colon inflammation) seen in both
conditions affects the whole colon, and if it has been present for more
than ten years. The risk is probably reduced by regularly taking
mesalazine (5-aminosalicylic acid), a medication that is widely used to
reduce the risk of relapse in these diseases. More info can be found at
www.canceriscurable.org
