Long-Term Follow-up of Risk of Cancer Among Twins
In a long-term follow-up study among approximately 200,000 Nordic twin individuals, there was an increased cancer risk in twins whose co-twin was diagnosed with cancer, with an increased risk for cancer overall and for specific types of cancer, including prostate, melanoma, breast, ovary, and uterus, according to a study published by Mucci et al in JAMA.
Refinement of primary and secondary cancer prevention strategies (ie, factors that would have the greatest influence on reducing cancer incidence and death) requires a detailed understanding of the contribution of genetic and environmental factors to disease pathogenesis. Large twin studies of cancer can provide insight into the relative contribution of inherited factors and characterize familial cancer risk by leveraging the genetic relatedness of monozygotic and dizygotic twins, according to background information in the article.
Study Findings
Lorelei A. Mucci, ScD, MPH, of the Harvard T.H. Chan School of Public Health, and colleagues estimated familial risk and heritability of cancer types among 80,309 monozygotic and 123,382 same-sex dizygotic twin individuals (n = 203,691) from the population-based registers of Denmark, Finland, Norway, and Sweden. Twins were followed up a median of 32 years between 1943 and 2010. There were 50,990 individuals who died of any cause, and 3,804 who emigrated and were lost to follow-up.
A total of 27,156 incident cancers were diagnosed in 23,980 individuals, translating to a cumulative incidence of 32%. Cancer was diagnosed in both twins among 1,383 monozygotic (2,766 individuals) and 1,933 dizygotic (2,866 individuals) pairs. Of these, 38% of monozygotic and 26% of dizygotic pairs were diagnosed with the same cancer type. There was an excess cancer risk in twins whose co-twin was diagnosed with cancer, with estimated cumulative risks that were an absolute 5% higher in dizygotic (37%) and an absolute 14% higher in monozygotic twins (46%) whose twin also developed cancer compared with the cumulative risk in the overall cohort (32%).
For most cancer types, there were significant familial risks and the cumulative risks were higher in monozygotic than dizygotic twins. Heritability of cancer overall was 33%. Significant heritability was observed for the cancer types of skin melanoma (58%), prostate (57%), nonmelanoma skin (43%), ovary (39%), kidney (38%), breast (31%), and corpus uteri (27%).
“The data provide strong evidence of an excess familial risk for 20 of the 23 cancer types, as shown by the comparison of familial risks for those cancers with the cumulative risk in the twin cohort overall,” the authors wrote.
The researchers noted that dizygotic pairs of twins are as genetically similar as siblings, so that familial risk estimates among dizygotic pairs are relevant for siblings who are born at separate times. “This information about hereditary risks of cancers may be helpful in patient education and cancer risk counseling,” they added.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
