Researchers have found that a class of immune-boosting oncology drugs, called checkpoint inhibitors, could cause fatal heart damage in rare instances, according to a report released Wednesday in the New England Journal of Medicine.

Checkpoint inhibitors have been approved by FDA to treat six types of cancer: bladder, kidney, lung, and head and neck cancer, as well as melanoma and Hodgkin lymphoma. Doctors are also using them to treat many other types of cancer, Denise Grady reports for the New York Times.

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The report in NEJM analyzed two case studies of melanoma patients that died of heart-related causes two weeks after receiving their first treatment with a combination of two drugs: Bristol-Myers Squibb's Opdivo and Yervoy. According to the report's disclosure, some Bristol-Myers' scientists co-authored the report, while other co-authors consult for the pharmaceutical company.

While the research focused only on those two drugs, lead author Javid Moslehi of Vanderbilt University School of Medicine said he believed two similar drugs on the market could pose similar risks. "My sense is that this is a class effect, not limited to one drug," he said.

According to the research, checkpoint inhibitors can cause the immune system to attack the heart. The effects are rare, however: As of April, only 18 cases of serious heart inflammation had been reported among 20,594 patients receiving Opdivo, Yervoy, or both.  

The heart inflammation was more severe and more common among patients who received both drugs, researchers wrote. That's because using both drugs increases the risk of overstimulating the immune system, according to Northwestern University's Jeffrey Sosman, who treated both of the patients who died. "The big question is, is there enough advantage to using the combination, which is much more toxic, than a single drug," he added.

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Michael Atkins, deputy director of the Georgetown-Lombardi Comprehensive Cancer Center, said that the heart issues are "alarming," but added that the rare heart effects should be treatable in most patients. "It just gives us a moment of pause," he said. "This is a rare event … but it's a particularly serious one." Moslehi said the findings shouldn't stop patients from taking the drugs, which he called "transformative." He said that researchers are "working to develop treatments for it. Our job is not to say the drugs are bad, but to say, 'How can we deal with it?'"

Moslehi added that "no one" had the heart issue "on their radar" so patients on the immunotherapy drugs were not regularly screened for cardiovascular problems.

The discovery of this side effect has prompted some hospitals to screen patients taking checkpoint inhibitors for cardiovascular problems. According to the Times, if the problem is caught early, steroids and other drugs may stop the patient's immune system from attacking the heart (Marchione, AP/STAT News, 11/2; Grady, New York Times, 11/2; American Association for Cancer Research, 9/20).

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