Study of twins reveals shared roles of genetics and environment in cancer risk

A new study of twins has uncovered the shared roles of genetics and environment in determining a person's risk of cancer.

According to Lorelei Mucci, an associate professor of epidemiology at the Harvard TH Chan School of Public Health in Boston, having an identical twin diagnosed with cancer increases the other twin's risk of developing not just that type but any form of cancer.

She added, this showed that some families carried a shared higher risk for any type of cancer, based on their genes.

"Different cancers may share an inherited susceptibility based on genetic factors," Mucci said. "This is an area that we're just learning about," reported.

She added, though that the influence of genetics varied widely depending on the type of cancer.

She added, for instance, testicular, skin and prostate cancers showed strong influenced of genetics, while lung, colon and rectal cancers appeared to be driven largely by environmental factors.

The researchers studied over 200,000 twins, both identical and fraternal, who hailed from Denmark, Finland, Norway and Sweden, who formed part of the Nordic Twin Study of Cancer. They were followed an average 32 years between 1943 and 2010.

However, just because one twin developed cancer did not mean that the other was certain to get the same cancer, or any cancer at all, according to the report in the Journal of the American Medical Association (JAMA).

Rather the increased risk of cancer was 14 per cent higher in identical pairs in which one twin was diagnosed with cancer.

Identical twins develop from the same egg and share the exact same genetic material, while fraternal twins, which develop from two eggs are genetically as similar as typical biological siblings. The corresponding risk of cancer in a twin whose co-twin was infected was 5 per cent higher.

The researcher found that when seen as a group, about one in three individuals developed cancer (32 per cent).