San Antonio resident Brittany Galan was diagnosed with leukemia when she was 6 weeks old. She underwent chemotherapy for two years and has had several health problems as a result of the treatment. (Tamir Kalifa for The Washington Post)

The rate of second malignancies in survivors of childhood cancer is declining — an improvement linked to reduced radiation treatment of the first disease, according to a new study.

The research, published Tuesday in the Journal of the American Medical Association, focused on new cancers — not recurrences — that occurred within 15 years of the original ones. The rate for such cancers fell from 2.1 percent for survivors diagnosed in the 1970s to 1.3 percent for those diagnosed in the 1990s.

For the same period, the percentage of pediatric cancer patients treated with radiation therapy fell from 77 percent to 33 percent, and the doses were ratcheted back.

The study was the latest to suggest that efforts to modify potentially toxic cancer treatments — including radiation and chemotherapy — are paying off in reduced “late effects.” These are serious and sometimes life-threatening complications, such as second cancers, heart problems and infertility, that can affect cancer survivors years later.

The research was based on data from the National Cancer Institute-sponsored Childhood Cancer Survivor Study, which tracks more than 30,000 survivors. The new analysis included more than 23,000 people treated over three decades.

Oncologists and researchers had long assumed that reducing radiation would benefit pediatric cancer survivors, said Gregory Armstrong, an oncologist at St. Jude’s Children’s Research Hospital in Memphis and the principal investigator of the CCSS. But the new paper demonstrates the link, said Armstrong, one of the authors of the study.

“We reduced radiation therapy and that reduced the risk,” he said.

Even so, childhood cancer survivors remain at risk for later malignancies. Survivors from the 1990s are four times as likely to be diagnosed with another cancer than their peers who were never sick with cancer. Those treated in the 1970s are six times as likely to develop another cancer. The most common second malignancies are breast and thyroid cancers.

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