According to the results of a new study, performed using twins, genes play a relatively small role in the development of most types of cancer. According to researchers, genes accounted for less than half of the risk of several types of cancer, with the rest of the risk explained by environmental factors, such as smoking, diet, infections and exposure to chemicals and radiation.
Twins are often used to study genetics, since identical twins have all the same genes, while fraternal twins usually share about half the same genes.
Researchers state that genes probably explain 27% to 42% of the risk of colorectal cancer, breast cancer and prostate cancer.
"We conclude that the overwhelming contributor to the causation of cancer in the populations of twins that we studied was the environment," the authors write.
The New England Journal of Medicine 2000;343:78-85,135-136.
