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Cancer in one twin indicates much higher risk for sibling

When one twin is diagnosed with cancer, a fraternal twin has a 37 percent chance of also developing cancer while an identical twin was found to have a 46 percent chance.
By Stephen Feller   |   Jan. 5, 2016 at 5:08 PM

BOSTON, Jan. 5 (UPI) -- A large study of Nordic twins found when a twin is diagnosed with cancer, the sibling has a significantly higher chance of developing any type of cancer.

Researchers at Harvard University found in the study, conducted with the University of Southern Denmark and University of Helsinki, that twins with any type of cancer often developed different types of cancer, suggesting an overall prevalence among families for the disease.

"Prior studies had provided familial risk and heritability estimates for the common cancers -- breast, prostate, and colon -- but, for rarer cancers, the studies were too small, or the follow-up time too short, to be able to pinpoint either heritability or family risk," said Lorelei Mucci, an associate professor of epidemiology at Harvard, in a press release.

In the study, published in the Journal of the American Medical Association, researchers at the three universities reviewed health records for 80,309 monozygotic and 123,382 dizygotic twins using the population-based health registries of Denmark, Finland, Norway, and Sweden. The twins had follow-ups at a median of 32 years between 1943 and 2010.

The researchers found a total of 27,156 cancers diagnosed in 23,980 people, or 23 percent of the study participants. Of the cancers, 38 percent of monozygotic and 26 percent of dizygotic twins had the same cancer. Among fraternal twins with one diagnosed with cancer, the other had a 37 percent chance of diagnosis. The risk among identical twins was 46 percent.

The overall heritability of cancer was 33 percent, however it was found to be especially strong for testicular cancer, melanoma, prostate cancer, non-melanoma skin cancer, ovarian cancer, kidney cancer, breast cancer, and uterine cancer.

"Findings from this prospective study may be helpful in patient education and cancer risk counseling," said Jaakko Kaprio, a researcher at the University of Helsinki.

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