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    Twins Show Some Families Carry Shared Cancer Risk

    Large review finds if one identical twin gets a cancer, the other is at increased risk for the disease as well

    WebMD News from HealthDay

    By Dennis Thompson

    HealthDay Reporter

    TUESDAY, Jan. 5, 2016 (HealthDay News) -- A new study of twins has shed light on the shared roles of genetics and environment in determining a person's risk of cancer.

    Having an identical twin diagnosed with cancer increases the other twin's risk of developing not just that type but any form of cancer, said lead researcher Lorelei Mucci, an associate professor of epidemiology at the Harvard T.H. Chan School of Public Health in Boston.

    This suggests that some families carry a shared increased risk for any type of cancer, based on their genes, she said.

    "Different cancers may share an inherited susceptibility based on genetic factors," Mucci said. "This is an area that we're just learning about."

    However, the influence of genetics varies widely depending on the type of cancer, Mucci added.

    For example, testicular, skin and prostate cancers were shown to be influenced strongly by genetics, while lung, colon and rectal cancers appeared to be driven largely by environmental factors, she said.

    The study involved more than 200,000 twins, both identical and fraternal, who hailed from Denmark, Finland, Norway and Sweden. These twins are part of the Nordic Twin Study of Cancer, and were followed an average 32 years between 1943 and 2010.

    Researchers compared identical twins with fraternal twins because identical twins share 100 percent of their genes, Mucci said, while fraternal twins are just like ordinary siblings and share on average about half of their genes.

    About one-third of the participants developed cancer during the study, and researchers found that, overall, twins are not more likely to develop cancer than the general population, Mucci said.

    But when one identical twin developed any cancer, the other twin carried a 14 percent increased cancer risk compared with the general population, the researchers found.

    By comparison, a fraternal twin's cancer risk increased only 5 percent if their sibling was diagnosed with cancer.

    These findings demonstrate that "cancer is not only due to genetics or environment alone but is due to a combination of the two," said Dr. Stephanie Bernik, chief of surgical oncology for Lenox Hill Hospital in New York City.

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