Before, cancer is believed to be based more on luck than genes or lifestyle. A landmark study involving twins, however, suggests one should never downplay genes.
Researchers from T. H. Chan School of Public Health in Harvard University, University of Helsinki, and University of Southern Denmark have come together to determine the familial risks of at least 23 types of cancers, including rare ones.
It turns out that if one of the twins develops cancer, the risk of the other to have any type of cancer goes up significantly, even among rare cancers such as stomach and ovarian cancer. Interestingly, too, the chances of having a different type of cancer are high.
For this study, the group looked into two factors: heritability, an assessment of the cancer risk associated with genes, and familial risk, or the measure of a person's risk for cancer.
To obtain the needed data, they worked with over 150,000 fraternal and identical twins from Nordic regions like Denmark and Finland who participated in a cancer study from 1943 to 2010.
The analysis then revealed that at least 3,000 pairs developed cancer on both twins. If one of the twins had cancer, the risk for the other to develop one went up by 37% among fraternal twins and 46% among identical twins. Further, among those with cancer, identical twins have 38% chance of having the same type of cancer, 26% for fraternal twins.
Testicular cancer, meanwhile, posed the highest familial risk as it increased by 12 times among fraternal and almost 30 times among identical twins. In terms of heritability, skin melanoma is the highest at 58% followed by prostate, non-melanoma skin cancer, ovarian, kidney, breast, and uterine cancer.
This new study is important since previous researches focused on genetic risk among common types of cancers. This is the first time that rare kinds are also considered. Moreover, since fraternal twins have a similar genetic predisposition to regular siblings, the results may indicate the shared familial risk within a family.
The study is now available in JAMA.