The study found that for women with “triple-negative” breast cancer, adding Keytruda to standard chemotherapy improved their odds of responding.
And in the months afterward, women treated with the drug were less likely to see their cancer come back.
The findings are encouraging in a disease that is challenging to treat, said Dr. Skip Burris, president of the American Society of Clinical Oncology.
“I think these results will be greeted enthusiastically by doctors and patients,” said Burris, who was not involved in the trial.
Triple-negative breast cancers account for about 10% to 15% of all breast cancers, according to the American Cancer Society. They are so called because the cancer‘s growth is not fueled by estrogen, progesterone or a protein called HER-2.
Unfortunately, Burris said, that means women with the disease are unlikely to benefit from the hormone therapies and “targeted” drugs that have greatly improved breast cancer survival for U.S. women.
Instead, the mainstays of treatment are surgery and chemotherapy.
On top of the lack of treatment options, triple-negative breast cancer is typically more aggressive than other forms of the disease, Burris said.
Most breast cancers related to the BRCA1 gene mutation are triple-negative. The tumors are also more common among younger women and African Americans.
Keytruda (pembrolizumab) belongs to a newer class of cancer drugs called immune checkpoint inhibitors. They work by releasing a particular “brake” on the immune system, which allows it to find and attack cancer cells.
The drugs are given intravenously, and approved for several cancers, including advanced cases of melanoma, lung, liver, bladder and stomach cancers.
And last year, the U.S. Food and Drug Administration approved a different immune checkpoint inhibitor — Tecentriq (atezolizumab) — to treat some women with advanced triple-negative breast cancer that has spread beyond the breast.
The new trial, published Feb. 27 in the New England Journal of Medicine, was funded by drugmaker Merck. It focused on women newly diagnosed with earlier-stage triple-negative cancer. The goal was to see whether Keytruda might help prevent recurrences and spread of the disease in the first place.