Young girls who receive full-chest radiation after contracting Wilms tumor, a rare childhood kidney disease, may face a much higher risk of developing breast cancer when they grow up, a new study finds.
The effects of radiation exposure boosted the chance of breast cancer nearly 30 times higher than expected, suggesting that current screening guidelines should be changed to ensure early diagnosis and treatment in female Wilms tumor survivors who received radiation therapy.
That’s according to a new analysis of data from the National Wilms Tumor Study, a longitudinal database that was started by Fred Hutchinson Cancer Research Center scientists 45 years ago and includes an estimated 70 percent to 80 percent of all cases that occur in the United States.
The study, published Monday in the journal Cancer, offers a warning about treatment for Wilms tumor, which can spread from the kidney to the lungs. In such cases, children are typically dosed with chest radiation of 12 Gray, the unit that measures absorbed radiation in the body, said Dr. Norman Breslow, a biostatistician with the University of Washington and Fred Hutch who has worked with the study since its inception. In the past, the standard dose was higher, 14 Gray.
At the time, most parents don’t object.
“What is probably true is that when a child is diagnosed with cancer, the parents are mainly concerned with curing that cancer,” Breslow said. “They’re not going to think about the long-term effects.”
That’s the job of Breslow and other statisticians, who examined records from nearly 2,500 females from the U.S. and Canada collected between 1969 and 1995. They revealed the largest number of breast cancer cases in Wilms tumor survivors seen to date, Breslow said.
“In female survivors, there was relatively little information available in the literature,” Breslow said. “Our study was able to provide that information because we’ve studied so many children for so long.”
The study included young women who had been treated for Wilms tumor during childhood and survived to age 15. It followed them into adulthood, as late as age 55. The study detected 29 cases of breast cancer among 28 patients, including one woman who developed the disease twice.
Among those was Michelle Douglas, 34, of Las Vegas, who was diagnosed with Wilms tumor when she was born. She didn’t know that she’d had radiation as a child, but now realizes she probably did.
“The only thing I remember is going through the X-ray machines,” she said. “They were really cold.”
Douglas, who works as a cocktail waitress, was diagnosed with breast cancer in her late 20s. Doctors treated her with chemotherapy and it appeared the disease was gone, but the cancer recurred, leading to a double mastectomy. Now, it has spread to her spine, Douglas said.
About 500 new cases of Wilms tumor are diagnosed in the U.S. each year, typically in children younger than age 6. Although it’s a rare disease, it is the most common type of kidney cancer in children, according to the American Cancer Society.
Standard treatment with radiation and chemotherapy has helped boost cure rates for Wilms tumor to nearly 90 percent, but it comes with a higher risk of secondary cancers, previous research has shown.
In the new study, more than 20 percent of Wilms tumor survivors who received chest radiation developed breast cancer by age 40. In women without the disease, the chance of developing breast cancer by 40 is less than 1 percent, Breslow calculates.
Researchers also found a moderate risk of breast cancer in women who had received abdominal radiation but no chest radiation.
The risk of breast cancer was about 28 times higher than expected in Wilms tumor survivors who had received chest radiation and six times higher than expected in those who received abdominal radiation. It was also twice as high as expected in patients who had received no radiation, the researchers found.
The magnitude of the increased breast cancer risk was unexpected and could lead to changes in the way Wilms tumor patients are screened and monitored, researchers said. Current guidelines recommend screening survivors who received 20 gray or more of radiation to the chest starting at age 25 or eight years after treatment.
But the new study clearly demonstrated higher risk at much lower levels of radiation, said Breslow.
“The recommendation is based largely on results of breast cancer occurring in survivors of childhood Hodgkin’s lymphoma,” he said. “They simply never had a large enough sample of children who received a standard dose of 12 Gray to the entire chest to know that this did, indeed, increase the risk of breast cancer.”
In an editorial accompanying the study, researchers from the Children’s National Health System in Washington, D.C., said that high-risk Wilms tumor survivors should start breast cancer surveillance with mammogram, breast MRI, or both, starting at age 25. But they also noted that research shows less than half of childhood cancer survivors at high risk for breast cancer actually follow through with recommended screening. They called for more education and awareness for survivors and providers.
For Douglas, knowing about her increased risk of breast cancer would have helped her and her oncologists make good decisions earlier, she said. Doctors couldn’t quite figure how her breast cancer was related to her childhood disease.
“I should have known to probably expect it,” she said. “It’s because I have scattered radiation from way back when.”
JoNel Aleccia is a staff writer at Fred Hutchinson Cancer Research Center. From 2008 to 2014, she was a national health reporter for NBC News and msnbc.com. Prior to that she was a reporter, editor and columnist for more than two decades at newspapers in the Northwest. Reach her at email@example.com.