There was significant excess familial risk among Nordic twins for cancer overall and for specific types of cancer, including prostate, melanoma, breast, ovary, and uterus, according to a study of 80,309 monozygotic and 123,382 same-sex dizygotic twin individuals in Denmark, Finland, Norway, and Sweden. Researchers found:

• 27,156 incident cancers were diagnosed in 23,980 individuals, for a cumulative incidence of 32%.

• Cancer was diagnosed in both twins among 1,383 monozygotic pairs and 1,933 dizygotic pairs.

• Of those, 38% of monozygotic and 26% of dizygotic pairs were diagnosed with the same cancer type.

• There was excess cancer risk in twins whose co-twin was diagnosed with cancer, with estimated cumulative risks that were 5% higher in dizygotic and 14% higher in monozygotic twins vs cumulative risk in the entire cohort.

• For most cancer types, there were significant familial risks, with higher risk for monozygotic vs dizygotic twins.

• Significant heritability was seen for cancers including skin melanoma (58%), prostate (57%), nonmelanoma skin (43%), ovary (39%), kidney (38%), breast (31%), and corpus uteri (27%).

Citation: Mucci LA, Hjelmborg JB, Harris JR, et al. Familial risk and heritability of cancer among twins in Nordic countries. JAMA. 2016;315(1):68-76. doi:10.1001/jama.2015.17703.