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.

JAMA, Jan. 5, 2016

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  1. Francine

    We’re the twins vaccinated at the same time .

  2. Bess

    I am suffering from tendonitis caused by Cepro and it keeps appearing in new places.
    I was prescribed three years ago and within 2 to 3 weeks began suffering. I now have 2 torn tendons in right shoulder and a newly affected in right wrist/hand. There was no patient warning at the time, which now there is. Why is the government allowing this to continue to be prescribed/sold? I would not wish this pain on my worst enemy!

  3. Susan B

    There may be other environmental issues not considered, such as the health, diet and exposure to toxins of the mother while pregnant with the twins. Also it must be assumed that the twins ate similar diets and were exposed to the same or very similar environment and toxins while growing up. Twins separated at birth would negate my second point, but not the first. Still, it is an intriguing study.

  4. Larry M

    Well, this seems to make sense but there are some confounding effects. You would have to limit the testing to identical twins raised in different homes to eliminate some of them.

    Let’s suppose there are identical twins (with genetics in common). They are raised in a household with common exposure to carcinogens (e.g., Chlordane and tobacco smoke). Then as late teens they leave home and are exposed to different environments as they make their own homes.

    Now suppose they both fall victim to the same cancer. How do you distinguish whether it was a genetic vulnerability or the common youthful exposure?

  5. teal

    This article fails to mention the component of being raised in the same womb for nine months where they would have been exposed to any toxin, air born or consumed by the mother such as pesticides, herbicides, cleaning chemicals, house hold goods out-gasing, etc. The review of this study is faulty.

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