After examining data on 44,788 pairs of twins, researchers report that, in most cases, environmental factors have the greatest effect on cancer risk. As reported in New England Journal of Medicine, researchers studied twins listed in Swedish, Danish, and Finnish registries, concluding that inherited genetic factors make a minimal contribution to cancer risk.
Heredity was judged to play no detectable role in cervical or uterine cancer. For lung cancer, genetics accounted for 26 percent risk. The remainder is due to environmental factors, such as smoking and other dangerous exposures. For cancers of the breast, ovary and prostate, the environmental component was estimated at 73 percent, 78 percent, and 58 percent, respectively.
Lichtenstein P, Holm NV, Verkasalo PK, et al. Environmental and heritable factors in the causation of cancer. N Engl J Med. 2000;343:78-85.