STOCKHOLM, SWEDEN. The relative roles of genes and environment in the development of cancer have been debated for years. It is now generally accepted that only 10-20 per cent of all cancers are genetically "preordained" while the remaining 80-90 per cent are caused by wrong diet, infections or by excessive exposure to carcinogens such as tobacco, alcohol, radiation, occupational toxins, and drugs. Swedish medical researchers at the Karolinska Institute now report that the "heritage factor" varies widely for different types of cancer. Their conclusions are based on an exhaustive study of the medical history of 44,788 pairs of twins, 15,669 of which were identical (monozygotic) twins. The researchers confirmed that the overall contribution of genetic constitution to the risk of all cancers is about 15 per cent. However, they also found that some cancers have a much larger genetic component than others. They estimate that 42 per cent of the total risk of prostate cancer is related to heritable factors, 27 per cent of breast cancer cases are related to genetic constitution, and 35 per cent of colorectal cancer cases may be genetically "preordained". Nevertheless, they point out that the absolute risk of an identical twin developing breast, prostate or colorectal cancer before the age of 75 years if their sibling has it is only somewhere between 15 and 18 per cent. For other cancers the risk is considerably smaller and for family members who are not twins the inherited component is of even less importance. The researchers conclude that the heritable component of cancer is not a very significant risk factor even among close relatives. Dr. Robert Hoover, MD of the National Cancer Institute lauds the new study and points out that it clearly shows the futility of trying to predict an individual's risk of cancer from their genetic constitution.
Lichtenstein, Paul, et al. Environmental and heritable factors in the causation of cancer: analyses of cohorts of twins from Sweden, Denmark, and Finland. New England Journal of Medicine, Vol. 343, July 13, 2000, pp. 78-85
Hoover, Robert N. Cancer - Nature, nurture, or both. New England Journal of Medicine, Vol. 343, July 13, 2000, pp. 135-36 (editorial)