NEW YORK -- Women's risk of developing breast cancer may increase as much as 20-fold if they were treated with chest radiation for malignancies as children or young adults, according to an analysis of studies.

By the time they are in their 40s, the women's incidence of breast malignancy may be 13 to 20 percent compared with about 1 percent for females generally, researchers said Monday in the Annals of Internal Medicine. A second study in the journal said both male and female survivors of childhood cancers die about a decade sooner.

The findings add to research showing the effects of childhood cancer and its treatment, said Kevin Oeffinger, one of the authors of the breast cancer study. As adults, these survivors should be aware of their health risks and work with doctors to prevent premature death, the researchers said.

"We still need radiation for treatment of many of the cancers," said Dr. Oeffinger, director of the Adult Long-Term Follow-Up Program at Memorial Sloan-Kettering Cancer Center in New York, in a telephone interview. "If a woman were treated with radiation to the chest area for a pediatric or young-adult cancer, [she] should talk to [her] doctor" about when to begin screenings for breast cancer, he said.

There are more than 300,000 childhood-cancer survivors in the United States, Dr. Oeffinger said. Treatments such as radiation can damage healthy cells while destroying malignant cells, according to the National Cancer Institute, based in Bethesda, Md. In children, this can prevent bones, tissues and organs from developing properly, leading to damage seen years later.

People who beat cancer as children face a risk of worse health over their lifetimes from heart disease, infertility and psychological ailments, the National Cancer Institute said.

As many as 55,000 women in the United States today were treated as children with moderate to high doses of radiation to their chest to fight lymphoma and other cancers, according to the breast-cancer study.

Dr. Oeffinger and colleagues at the University of Chicago, St. Jude Children's Research Hospital in Memphis, Tenn., and other institutions wanted to determine the breast cancer risk for such survivors. The researchers analyzed 11 studies that had data on 7,000 women who received chest radiation as children or young adults from 1960 to 2000.

Women who received chest radiation had a chance of developing breast cancer by the age of 40 to 45 that ranged from 13 percent to 20 percent, depending on the dose of radiation therapy they received as children, according to the analysis. Women in the general population have a 1 percent likelihood of getting breast cancer by age 45, the study said.

The increased risk for breast cancer was seen as soon as eight years after the chest radiation was given and didn't level off as the women grew older, the researchers said.

The researchers also wanted to assess the benefits and risks for screening the women from age 25 throughout their lifetime for breast cancer, Dr. Oeffinger said. Results suggested the advantage of early cancer detection outweighed the risk of more radiation from screening X-rays. He said the best results came from combining mammograms with magnetic resonance imaging, or MRI.

In the second study on lifespan, Jennifer Yeh, a research fellow at Harvard School of Public Health in Boston, developed a mathematical model to predict the longevity of survivors of childhood cancers, including leukemia, brain and bone tumors, and lymphoma.

The estimates covered both men and women, and varied by diagnosis, ranging from kidney-tumor survivors' dying four years sooner than the general population to brain and bone tumor survivors' dying almost 18 years earlier.

That means as much as a 28 percent reduction in their life expectancy, said Dr. Yeh, who worked with colleagues from Harvard and Emory University in Atlanta. "Survivors of childhood cancer continue to face excess mortality risks in their adult years," said Dr. Yeh in an e-mail. A childhood-cancer survivor who reaches the age of 40 has a 3.3-fold higher risk of dying before the age of 50 than those in the general population, according to the research.

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