The combination did cause side effects, including fatigue and neutropenia -- a decrease in important disease-fighting white blood cells. But these "were manageable side effects," Finn said.
Still, Blackwell said, the safety and ultimate effectiveness of the therapy "remain to be validated."
According to the American Cancer Society, the average U.S. woman has a 12 percent chance of developing breast cancer in her lifetime. Death rates from the disease have dropped in recent decades because of better treatments and earlier detection, experts said.
Learn more about breast cancer from the American Cancer Society.
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