Cancers and genetic factors

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 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 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.


Overall, one in three people in the study developed cancer over the course of a lifetime. Cancer was diagnosed in both twins for 3,316 of the pairs, in whom the same cancer was diagnosed among 38% of the identical twins and 26% of the fraternal twins. The researchers estimated that, when one fraternal twin was diagnosed with any cancer, the co-twin's risk of getting cancer was 37%; among identical twins, the risk jumped to 46%. One of the strongest familial risks was observed for testicular cancer. The researchers found that a man's risk of developing this disease was 12 times higher if his fraternal twin developed it, and 28 times higher if his genetically identical twin developed it.


Given the fact that fraternal twins are similar genetically to siblings who aren't twins, the finding of excess cancer risk among fraternal twin pairs can provide information about an increased cancer risk for families in which one sibling gets cancer.


The researchers also found that the heritability of cancer overall was 33%. Significant heritability was found for skin melanoma (58%), prostate cancer (57%), non-melanoma skin cancer (43%), ovarian cancer (39%), kidney cancer (38%), breast cancer (31%), and uterine cancer (27%).

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