How much does genetics factor into cancer risk? A new study of twins shows that both genetics and environment play a role. Having a twin with cancer increases the other twin’s chances of developing not only that same type of cancer but any form of cancer. This fact leads scientists to conclude that some families have a shared increased risk for any type of cancer because of their genes.
The new study examined more than 200,000 identical and fraternal twins from Denmark, Norway, Finland, and Sweden who were part of the Nordic Twin Study of Cancer. Twin sets were followed for an average of 32 years between 1943 and 2010. The lead author of the study was Lorelei Mucci, an associate professor of epidemiology at the Harvard T.H. Chan School of Public Health in Boston.
Mucci and her team found that twins were not more likely to develop cancer than the rest of the population. The researchers compared identical twins with fraternal twins because identical twins share all genes, but fraternal twins share only about half of their genes. This difference in shared genes made a significant impact on cancer risk when one twin developed cancer.
About one in every three participants in the study developed cancer. However, if one identical twin developed cancer, the other twin had a 14 percent increased cancer risk compared to the general population. Fraternal twins’ cancer risk increased only about five percent if their twin developed cancer.
The results of the study show that cancer risk is influenced by genetics and environment. Stephanie Bernik, M.D., chief of surgical oncology for Lenox Hall Hospital in New York city, stated, “If cancer was simply genetic, identical twins would be affected by cancer equally. Although there was an increased risk of cancer amongst twins, there was not a 100 percent correlation, indicating that environmental factors also play a part in the development of cancers.”
The researchers also discovered that genetics do not affect the risk of all cancers equally. Testicular, skin and prostate cancers were strongly influenced by genetics, but lung, colon and rectal cancers seemed to be more affected by environmental factors. In melanoma, for example, genetics was a strong influence, increasing risk by 58 percent. In the case of colon cancer, genetics played a smaller role, at only 15 percent.
Because cancer is influenced by both genetics and environment, it is important to be aware of your own family history. Talk to your family members and ask questions about the types of cancers that run in your family. Colon cancer actually is more influenced by family history than previously thought, so take a look at our infographic at the bottom of our Family History page to get a visual picture of how genetics influences your risk for colon cancer. Remember, there are several risk factors for colon cancer that you can control, so decrease your risk for colon cancer by quitting smoking, limiting alcohol, eating a low-fat and high-fiber diet, exercising regularly, and getting colon screenings at appropriate intervals as recommended by your doctor (Source: US News).