Childhood cancer survivors at increased risk of breast cancer

Young women who were treated for cancer as children have a greater chance of developing breast cancer if their treatment included chest radiation, if they initially had cancer of the bones, muscles, or connective tissue, or if they have a family history of breast cancer, according to a new study led by researchers at Harvard-affiliated Dana-Farber Cancer Institute and Children’s Hospital Boston.

As the number of childhood cancer survivors grows, the new study – published in the Oct. 19 issue of the Annals of Internal Medicine – should help physicians determine which are at increased risk for breast cancer and can benefit most from screening and prevention techniques, the authors say.

“We’ve known for many years that childhood cancer survivors have higher rates of breast cancer than the general population,” said lead author Lisa Kenney of Dana-Farber and Children’s. “But, other than prior treatment with chest radiation, it hasn’t been clear what factors increase survivors’ risk for the disease.”

Kenney and her colleagues analyzed data from the Childhood Cancer Survivor Study (CCSS) – a national study of children diagnosed with cancer from 1970 to 1986 who survived at least five years after treatment – for clues to the development of adult breast cancer. Of the more than 6,000 young women participating in the study, investigators identified 95 who were diagnosed with breast cancer.

As expected, breast cancer was more prevalent than normal among survivors who had been treated with chest radiation during childhood or adolescence. (Radiation can damage cells’ DNA in ways that promote cancer.) Breast cancer rates were also elevated among women who had survived bone or soft-tissue sarcomas (cancers affecting muscles, tendons, and ligaments) but hadn’t received chest radiation. Survivors who had a family history of breast cancer had higher breast cancer rates as well, regardless of whether they’d received radiation therapy as children.

“Clearly, girls treated with chest radiation are not the only survivors of childhood cancer who are at increased risk for breast cancer,” said Kenney, who is also an instructor in pediatrics at Harvard Medical School (HMS). “What we’ve learned from this study suggests that some survivors have a genetic tendency to developing breast cancer as young women.”

Among the study’s other findings was that women who had received pelvic radiation for childhood cancer had lower breast cancer rates, on average, than women in the general population. Researchers explain this pattern by noting that pelvic radiation shuts down the ovaries’ production of estrogen, a hormone that can spur the growth of breast cancer cells. Women treated with chest radiation who then developed thyroid disease were also found to have higher rates of breast cancer.

“Physicians should make a point of assessing breast cancer risk in all young women who are survivors of childhood cancer,” said senior author and HMS Associate Professor of Pediatrics Lisa Diller of Dana-Farber and Children’s. “By offering early screening to survivors at increased risk, we can increase the chances that breast tumors will be detected and treated at the earliest stages, when they are most susceptible to therapy.”