Older black women with human epidermal growth factor receptor 2 (HER2)–positive breast cancer are less likely than their white peers to receive targeted therapy with trastuzumab (Herceptin), a U.S. study suggests.

When researchers examined data from Medicare, the U.S. health program for people over age 65, they found just 40 percent of black women with HER2-positive tumors received trastuzumab, compared with 50 percent of white women.

"A very substantial racial disparity exists," said study leader Dr. Katherine Reeder-Hayers of the University of North Carolina Chapel Hill Lineberger Comprehensive Cancer Center.

"Although we don't know for sure why this is happening, the fact that the treatment is relatively new, expensive, and lengthy may all be contributing," Reeder-Hayes added by email.

Reeder-Hayes and colleagues looked data on about 1,400 women diagnosed with HER2-positive breast cancer in 2010 and 2011 and examined how many of them received trastuzumab in the year after their diagnosis.

After adjusting for tumor characteristics, poverty and patients' other medical problems, black women were 25 percent less likely to get trastuzumab than white women, researchers report in the Journal of Clinical Oncology, online April 7.

It's possible that some of the women didn't receive trastuzumab because of the risk of heart damage and other side effects that come with the drug, said Erica Warner of Massachusetts General Hospital.

"I think concerns about toxicity, particularly cardiotoxicity, in women (who) may have other chronic diseases and limited life expectancy gives some clinicians pause," Warner, who wasn't involved in the study, said by email.

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Because many women over age 70 don't receive chemotherapy or targeted treatments like trastuzumab, the racial disparities found in the study might not look the same among younger women, noted Dr. Richard Bleicher of Fox Chase Cancer Center in Philadelphia.

"At the extremes of older age, patients may die of other causes," Bleicher, who wasn't involved in the study, said by email. "That having been said, if the patient is appropriate for it, it should be offered."

One limitation of the study is that Medicare data can't provide a full picture of medical conditions that might influence whether doctors give women trastuzumab, the authors note. In particular, they lacked data on heart conditions that might make this treatment too risky.

"There is no way to fully understand what was recommended to patients, whether they refused treatment, or whether there was some other barrier," said Dr. Rachel Freedman of the Dana-Farber Cancer Institute.

Still, many women in the study were probably under-treated, and the racial disparities in trastuzumab therapy are consistent with earlier research, Freedman, who wasn't involved in the study, added by email.

"The patterns observed for trastuzumab are not that different from disparities observed for most health care," Roshan Bastani, director of cancer disparities research at the University of California, Los Angeles Jonsson Comprehensive Cancer Center, said by email.

"Those less likely to receive optimal care tend to be poor, ethnic minority and the elderly," said Bastani, who wasn't involved in the study. "The consequence of this is that these groups are deprived the opportunity to benefit from scientific advances in care and are at increased risk for poorer outcomes."