Twins share cancer risk: Study

A twin sibling diagnosed with cancer poses an excess risk for the other to develop any form of the disease, a new Harvard study has found.

An excess familial risk was seen for almost all of the cancers, including common cancers such as breast and prostate cancer, but also more rare ones such as testicular cancer, head and neck cancer, melanoma, ovarian and stomach cancer.

It also showed, for the first time, that in twins where both developed cancer, each twin often developed a different type of cancer suggesting that in some families there is a shared increased risk of any type of cancer.

"Prior studies had provided familial risk and heritability estimates for common cancers, but for rarer cancers the studies were too small, or the follow-up time too short, to pinpoint either heritability or family risk," said Lorelei Mucci, associate professor of epidemiology at Harvard.

Familial risk of cancer is a measure of the cancer risk in an individual. The study also looked at heritability of cancer, a measure of how much of the variation in cancer risk of the population is due to genetic factors.