Researchers have been debating the respective roles of genetics and environment on cancer for decades. This question is sometimes framed as “nature or nurture,” and the general consensus is that usually it is probably both. But to what extent?
A new study of Scandinavian twins suggests that overall about a third of cancers may be attributed to genetics. Over 200,000 identical and fraternal twins from Denmark, Finland, Norway and Sweden participated in the study. The average follow-up was a bit more than three decades.
What Did Scientists Learn from Twins with Cancer?
The differences between the cancer rates of fraternal and identical twins gave the scientists a way to tease out how much of the risk was hereditary, since identical twins share all the same genes. Fraternal twins, like other siblings, share half their genes.
Some Cancers Have an Especially Strong Familial Link:
For certain malignancies, such as testicular cancer or melanoma, the genetic component is especially strong. If one man developed testicular cancer, his fraternal twin was 12 times more likely than an unrelated person to develop this cancer. The risk skyrocketed to twenty-eight times higher in an identical twin.
In the case of melanoma, the incidence in the general population is roughly one percent. If, on the other hand, an identical twin developed melanoma, the second twin was at a 20 percent risk of also coming down with this life-threatening skin cancer.
Other cancers that seem to have a strong familial component include those of the prostate, breast, uterus and ovaries.