New study finds familial risk and heritability of cancer among twins

The researchers studies 23 different types of cancer, including common cancers such as breast and prostate cancer, as well as rare cancers like testicular cancer, melanoma, head and neck cancer, ovarian and stomach cancer.

Though this study is a twin study, the data can be extrapolated to inform decisions about cancer for other types of family members.

A new study suggests that if one twin develops cancer, the other has a higher risk of doing so.

The study also examined the passing of cancer from generation to generation to determine how much of a risk of developing cancer is from genetic factors.

The group, led by Lorelei Mucci, of the Harvard T.H. Chan School of Public Health, looked at the medical records of more than 200,000 twins, both identical and fraternal, born in Denmark, Finland, Norway, and Sweden between 1943 and 2010.

The twins were followed over an average of 32 years for the study.

They found that overall, one in three people in the study developed some type of cancer over their lifetime. Unfortunately, it seems like developing cancer may be one of the qualities both identical and fraternal twins share. Twins can either be identical (monozygotic), meaning that they can develop from just one fertilized egg, or fraternal (dizygotic), meaning that they can develop from two separate zygotes, each fertilized by separate sperm cells. 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%. Moreover, since fraternal twins have a similar genetic predisposition to regular siblings, the results may indicate the shared familial risk within a family.

Before, cancer is believed to be based more on luck than genes or lifestyle.

Researchers also found that the heritability of cancer overall was 33 per cent. Significant heritability was found for skin melanoma (58 per cent), prostate cancer (57 per cent), non-melanoma skin cancer (43 per cent), ovarian cancer (39 per cent), kidney cancer (38 per cent), breast cancer (31 per cent), and uterine cancer (27 per cent). Refinement of primary and secondary prevention strategies (i.e., 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 (the origination and development of a disease).

“This study was possible given the unique databases in the four Nordic countries, and will be a future resource to solve other complex questions in cancer”, said Hans-Olov Adami, adjunct professor of epidemiology at Harvard Chan School and co-senior author of the study.

“This information about hereditary risks of cancers may be helpful in patient education and cancer risk counseling”, the authors write.

“It was surprising that the estimate of heritability of melanoma was the largest of all of the studied cancers”, Mucci said. “If you have a brother who developed lung cancer, even though your risk is higher, you can still lower your risk by quitting smoking”.