CHICAGO -- Women treated with chest radiation for cancer when they were girls have a higher risk of developing breast cancer than previously thought, doctors warn.

Even lower doses of radiation therapy posed a risk for survivors of a childhood cancer, something not known before. That means more women might need to be screened starting at age 25.

"We find that by age 50, approximately 30 percent of women treated with radiation for Hodgkin lymphoma" as girls have developed breast cancer, said Chaya Moskowitz of Manhattan's Memorial Sloan-Kettering Cancer Center who led the study.

That is far higher than the 4 percent rate for the general population, and compares with the rate in women who have mutations in inherited BRCA genes that increase risk. Among women who had chest radiation for any type of childhood cancer, 24 percent developed breast cancer by age 50.

The study was presented yesterday at an American Society of Clinical Oncology conference in Chicago.

Radiation treatment has saved countless children from lymphoma, leukemia, soft-tissue tumors and other cancer types, but it can damage the DNA of healthy cells, too, and lead to cancer decades later.

Children treated today get much lower doses and to much smaller areas of the body than kids did in 1970 to 1986 when the women in this study were girls.

The new study finds higher risk even among those who got moderate doses. That means another 7,000 to 9,000 women may need screening now, said Dr. Paula Ryan, a breast cancer specialist at Fox Chase Cancer Center in Philadelphia.

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