The familial risk and heritability of several types of cancer in a large population of identical and fraternal twins was the subject of a recent long-term study, revealing that having a twin diagnosed with cancer means a significant higher risk for the other twin to develop any type of cancer.
A significant hereditability was found for certain types of cancer, such as skin melanoma. The research paper, “Familial Risk and Heritability of Cancer Among Twins in Nordic Countries,” was published in The Journal of the American Medical Association.
Genetic analyses in population-based studies are extremely valuable because they allow cancer risk predictions and heritability estimates, helpful in patient education and cancer risk counseling. Importantly, large studies with twins can help scientists determine the overall contribution of genetic factors in the incidence of cancer, due to the genetic link of identical and fraternal twins and exposure to similar environmental factors.
“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,” Lorelei Mucci, associate professor of epidemiology at Harvard Chan School and co-lead author of the study, said in a press release.
Researchers analyzed approximately 200,000 fraternal and identical twins in the population-based registers of Denmark, Finland, Norway, and Sweden, with a median follow-up of 32 years, between the years 1943 and 2010. The main outcome of the study was cancer incidence by measure of familial risk (risk of cancer in an individual) and heritability (proportion of variance in cancer risk due to individual genetic differences).
The results showed that, in the assess population, there was a cancer incidence of 32 percent. Cancer was diagnosed in both twins for 3,316 of the pairs, in whom the same cancer was diagnosed among 38 percent of the identical twins and 26 percent of the fraternal twins.
When one of the twins developed cancer, researchers estimated that the other had an increased risk of 37 percent for fraternal twins or 46 percent for identical twins. Overall, for most cancer types, familial risks were significant and cancer risk was higher in identical twins.
Overall heritability of cancer was of 33 percent and significant heritability was observed for skin melanoma (at 58 percent), prostate cancer (57 percent), non-melanoma skin cancer (43 percent), ovarian cancer (39 percent), kidney cancer (38 percent), breast cancer (31 percent), and uterine cancer (27 percent).
“Because of this study’s size and long follow-up, we can now see key genetic effects for many cancers,” said Jacob Hjelmborg, from the University of Southern Denmark and co-lead author of the study.
“This study was possible given the unique databases in the four Nordic countries, and will be a future resource to solve other complex questions in cancer,” said Dr. Hans-Olov Adami, co-senior author of the study.