Women who were treated with chest radiation during their childhood may be at a higher risk of developing breast cancer than previously thought, doctors warn.

A new study showed even low doses of radiation pose a risk for survivors.  With this new information, more women might need to begin screening for breast cancer 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, a biostatistician at Memorial Sloan-Kettering Cancer Center in New York who led the study.

That is far higher than the 4 percent rate for the general population, and is comparable to 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 to be presented Monday 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.

A federally funded study has been tracking more than 1,200 of them, and researchers used a second study of relatives of women with breast cancer to compare the odds of developing breast cancer among various groups such as those with BRCA gene mutations.

Guidelines currently urge annual screening with mammograms and MRI scans starting at age 25 for women who had radiation therapy totaling 20 Grays — a measure of how much radiation is absorbed. About 50,000 U.S. women are in that category.

The new study finds higher risk even among women who received more moderate doses — 10 to 19 Grays — as girls.

That means another 7,000 to 9,000 women also may need screening now, said Dr. Paula Ryan, a breast cancer specialist at Fox Chase Cancer Center in Philadelphia who had no role in the work.

"The important thing is, they've survived the cancer" that might have killed them as children, but they now should be closely followed to catch any second cancers early, when they are most treatable, she said. "They're a group that may be vulnerable."

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