A large new study on twins has found that having a twin sibling diagnosed with cancer may show a risk for the other twin to develop cancer as well. Among the 23 different types of cancer studied, an excess familial risk was discovered for almost all of the cancers, including common cancers such as breast and prostate cancer, but also more rare cancers such as testicular cancer, head and neck cancer, melanoma, ovarian and stomach cancer.
The study, led by researchers at the Harvard T.H. Chan School of Public Health, the University of Southern Denmark, and the University of Helsinki, is the first to inform people of family risks for these and other rarer cancers. The study showed, that if twin pairs where both to developed cancer, each twin, would most often developed a different type of cancerwhich suggests that, in some families, there is a shared increased risk of any type of cancer.
Prior studies had provided familial risk and heritability estimates for the common cancersbreast, prostate, and colonbut, 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, associate professor of epidemiology at Harvard Chan School and co-lead author of the study.
The study also looked at heritability of cancer. Findings from this prospective study may be helpful in patient education and cancer risk counseling," said Jaakko Kaprio, from the University of Helsinki and co-senior author of the study.
The researchers looked at more than 200,000 twins, both identical and fraternal. The Twins Studied were followed over an average of 32 years. Overall, one in three people in the study developed cancer over the course of a lifetime. Cancer was diagnosed in both twins for 3,316 of the pairs, in whom the same cancer was diagnosed among 38% of the identical twins and 26% of the fraternal twins. The researchers estimated that, when one fraternal twin was diagnosed with cancer, the sibling twin's risk of getting cancer was increased to 37%. In identical twins, the risk jumped to 46%. One of the strongest familial risks had been seen in testicular cancer. The researchers found that a man's risk of developing this disease was 12 times higher if his fraternal twin got it, and 28 times higher if his identical twin developed it.
Given the fact that fraternal twins are similar, the finding of excess cancer risk among fraternal twin pairs can provide information about an increased cancer risk for families in which one sibling gets cancer. The researchers also found that the heritability of cancer overall was 33%. Significant heritability was found for skin melanoma (58%), prostate cancer (57%), non-melanoma skin cancer (43%), ovarian cancer (39%), kidney cancer (38%), breast cancer (31%), and uterine cancer (27%).
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 Hans-Olov Adami, adjunct professor of epidemiology at Harvard Chan School and co-senior author of the study.
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