June 4, 2012 (Chicago) -- Girls treated with radiation for childhood cancers are at elevated risk of developing breast cancer in mid-life -- even if the radiation dose was relatively low, researchers say.
"We were surprised to find that women treated with radiation to the chest during childhood have a risk of developing breast cancer that is comparable to that of women who are carriers of the hereditary BRCA mutations," says Chaya Moskowitz, MD, of Memorial Sloan-Kettering Cancer Center in New York City.
Moskowitz and colleagues analyzed data from more than 1,200 women treated with radiation for childhood cancers and found that by age 50, 24% had been diagnosed with breast cancer. Among survivors of Hodgkin lymphoma -- who were treated with high doses of radiation that are no longer used -- the rate was 30%.
By comparison, about 31% of women who carry a mutation in the BRCA1 gene, which most doctors recognize as a known risk factor, are diagnosed with the disease by age 50, she says. Among women in the general population, the rate is 4%.
Previous studies have shown that women treated with radiation to the chest as children are at increased risk for breast cancer, Moskowitz says. But this is the first study to show that risk is comparable to carrying BRCA mutations, she tells WebMD.
It has also not been clear how lower levels of radiation used to treat pediatric cancers other than Hodgkin's disease affect breast cancer risk, Moskowitz says.
She notes that guidelines developed by the National Cancer Institute-sponsored Children's Oncology Group recommend that women treated with 20 grays -- a dosage measurement -- or more radiation to the chest begin annual mammograms and breast MRI scans at age 25, younger than recommended for average-risk women.
But the study showed that women exposed to between 10 and 19 grays are also at heightened risk and therefore may benefit from early breast cancer screens, Moskowitz says.
Approximately 50,000 women in the U.S. have been treated with 20 grays or higher, and an additional 7,000 to 9,000 have been exposed to 10 to 19 grays.
The findings were presented here at the annual meeting of the American Society of Clinical Oncology (ASCO).
12 Million Cancer Survivors
"These are rather striking data," says Nicholas Vogelzang, MD, of the Comprehensive Cancer Centers of Nevada in Las Vegas and US Oncology. He was not part of the study.
"We have an obligation to those many thousands and thousands of young women we treated years ago. Hopefully this will increase our awareness of [the] need for mammogram screening of this population," he says.
ASCO President Michael P. Link, MD, says that once active cancer treatment ends, survivors typically receive ongoing follow-up care from their primary care doctors.
"Patients should empower themselves and bring a summary of treatment they have received to their doctors," says Link, the Lydia J. Lee professor in pediatric cancer at Stanford University School of Medicine.
He notes there are nearly 12 million cancer survivors in the U.S., up from three million in the 1970s.
The work was supported by grants from the National Cancer Institute.
These findings were presented at a medical conference. They should be considered preliminary, as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.