Twin Study Reveals Increased Risk Of Familial Cancers

When a twin is diagnosed with cancer, the sibling has a much higher probability of developing cancer as well, according to a recent study.

Researchers at Harvard University, the University of Helsinki and the University of Southern Denmark worked together--finding that for the first time, a study showed that in twin pairs that developed cancer, each twin often developed a different type of cancer; the findings suggest that some families may actually carry a shared, increased risk for any type of cancer.

"Prior studies had provided familial risk and heritability estimates for the common cancers--breast, prostate, and colon--but, for rarer cancers, the studies were too small, or the follow-up time too short, to be able to pinpoint either heritability or family risk," said Lorelei Mucci, associate professor of epidemiology at Harvard Chan School and co-lead author of the study, in a news release.

During the study, researchers reviewed health records for 80,309 monozygotic and 123,382 dizygotic twins using the population-based health registries of Denmark, Finland, Norway, and Sweden. The twins had follow-ups at a median of 32 years between 1943 and 2010.

They found a total of 27,156 cancers diagnosed in 23,980 people or approximately 23 percent of the study participants. Of the cancers, 38 percent of monozygotic and 26 percent of dizygotic twins shared the same type of cancer. However, among fraternal twins, researchers found that when one twin was diagnosed with cancer, there was a 37 percent increased risk of a cancer diagnosis in the other twin with a 46 percent increased cancer risk among identical twins.

Previous studies have shown how cancer risk may be due to a number of environmental factors and personal lifestyle choices. However, some rarer types of cancer are based primarily on genetic factors. The findings showed that cancer heritability is about 33 percent, with a much higher risk coming from non-melanoma types of skin cancer, ovarian skin cancer, testicular cancer, prostate cancer, kidney cancer, breast cancer and uterine cancer.

The study is published in JAMA (Journal of the American Medical Association.)

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