A Swedish study of nearly 71,000 adopted people has used data from both their natural and adoptive parents to find that family history is a greater risk factor than lifestyle for developing breast, prostate, or colorectal cancer.
The genetic factors behind these three major cancers are well established, but this large survey of data published in the European Journal of Cancer has looked a unique group of people in a bid to disentangle familial risk from environmental factors.
By looking at adoptees, the researchers were able to see how being raised in an environment that was independent of hereditary genetics - being brought up by adoptive parents - revealed the true extent of the biological influence exerted by the genes of their real parents.
In effect, the study separated out the cancer effects of family history versus those of the environment.
If a person's biological parent had cancer, there was an 80-100% higher chance of them developing the same disease than if their natural parents were free of the cancer.
Yet the history of adoptive parents had no influence on the risk of developing cancer. If an adoptive parent had cancer, there was no increased effect on the adoptee.
The study was led by Bengt Zoller, a reader at Lund University in Sweden. Dr. Zoller says:
"The results of our study do not mean that an individual's lifestyle is not important for the individual's risk of developing cancer, but it suggests that the risk for the three most common types of cancer is dependent to a greater extent on genetics."
The study also found that adoptees who had a biological parent with cancer developed the disease at a younger age than those without a biological parent with the same cancer. This effect was not seen in relation to adoptive parents, however - whose cancer had no influence on the adoptees' age of disease onset.