A large new study of twins has found that having a twin sibling diagnosed with cancer poses an excess risk for the other twin to develop any form of cancer. Among the 23 different types of cancer studied, 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 cancers such as testicular cancer, head and neck cancer, melanoma, ovarian, and stomach cancer.
The study, led by researchers at the Harvard T.H. Chan School of Public Health, the University of Southern Denmark, and the University of Helsinki, is the first to provide family risk estimates for these and other rarer cancers. The study also showed, for the first time, that in twin pairs where both developed cancer, each twin often developed a different type of cancer — which suggests 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 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 Dr. Lorelei Mucci, associate professor of epidemiology at Harvard Chan School and co-lead author of the study.
The study was published online January 5 in JAMA (Journal of the American Medical Association).
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 populations is due to genetic factors.
The researchers looked at more than 200,000 twins, both identical and fraternal, in Denmark, Finland, Norway, and Sweden, who participated in the Nordic Twin Study of Cancer and were followed over an average of 32 years between 1943 and 2010. Large twin studies can help scientists assess the relative contribution of inherited factors in cancer and characterize familial cancer risk by taking into account the genetic relatedness of identical and fraternal twins. Read more