When an identical twin has cancer his sibling has 46 percent more chances to also develop the disease
Familial risk of cancer has been studied by researchers in Nordic Countries.
A new study published in JAMA on January 5 has studied twins to find out more about the familial risk of cancer. Their results show that when one of the twins is diagnosed with cancer the risk of cancer for the second twin increases dramatically.
The increased risk of cancer has been confirmed in all of the 23 types of cancer studied, including common types such as prostate and breast cancer but also more rare types of cancer such as stomach cancer, testicular or ovarian cancer, head and neck cancer and melanoma.
The study is a joint effort of researchers from Harvard University, from the University of Helsinki and the University of Southern Denmark. According to its authors it is the first study to estimate the family risk for all these types of cancer.
One of the most interesting first-time findings of the study was that when both of the twins developed cancer each of them developed a different type. This finding shows that in some families the increased risk of cancer is for any type of cancer and not a specific one as it was believed until now.
Harvard Chan School’s professor of epidemiology Lorelei Mucci who is also one of the co-authors of the study explains that previous studies estimated the heritability of common types of cancer such as breast, colon and prostate cancer but studies on rarer types of cancers were too small to provide estimations regarding the heritability or the family risk of developing cancer.
The study analysed data from 200,000 identical and fraternal twins between 1943 and 2010 who participated voluntary in the Nordic Twin Study of Cancer in Sweden, Norway, Denmark and Finland.
This very large database of twins helped scientists estimate the contribution of inherited factors in the development of cancer and also to assess the familial risk of cancer by studying the twins’ genetic relatedness.
Results of the study show that one in three people developed cancer and in 3,316 pairs both of the twins have been diagnosed with cancer. Among those 38 percent were identical twins and 26 percent were fraternal twins. This made it possible for researchers to estimate that the risk of cancer for a person whose fraternal twin has been diagnosed with cancer is about 37 percent and when the identical twin has been diagnosed the risk of the other twin is about 46 percent.
The overall heritability of cancer was 33 percent. The most prevailing heritability was observed in skin melanoma – 58 percent, followed by prostate cancer – 57 percent, skin cancer other than melanoma – 43 percent, ovarian cancer – 39 percent, kidney cancer – 38 percent, breast cancer – 31 percent and uterine cancer – 27 percent.
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