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The immunotherapy drug pembrolizumab (Keytruda) — is already approved by the U.S. Food and Drug Administration for other forms of cancer—has been found to be effective in patients with metastatic triple negative breast cancer, according to an international clinical trial led by New York University (USA).

Background: Triple negative breast cancer (TNBC), which represents approximately 15 percent of all breast cancer diagnoses, is the most deadly form of the disease. Because it tests negatively for estrogen and progesterone receptors, it is unresponsive to hormonal therapies. Recurrence is not uncommon and often leads to metastases in other organs. Currently, metastaticTNBC is treated with chemotherapy, which is typically associated with significant toxicity and numerous side effects. Conversely, the side effects of pembrolizumab are much less frequent and more tolerable

The Study: This clinical trial (multisite trial; 17 medical centers across 4 continents) looked at the innovative immunotherapy drug pembrolizumab. The first group (A)  included 170 patients who had had lots of previous treatment for a particularly aggressive form of breast cancer (triple negative, or estrogen- / progesterone -receptor negative and HER2 negative). Patients were not required to have expression of a protein known as PD-L1 (programmed death receptor ligand 1). The second group (B) included 52 patients with PD-L1-positive cancer who received pembrolizumab as their first treatment following the diagnosis of cancer spread.

Here are the results: In group A, pembrolizumab shrank cancers by more than 30 percent in 5 percent of patients, and stabilized the disease in 21 percent. Of the patients who had tumor reduction, all lived beyond a year. In group B (those who got the drug as first-line therapy), those who received pembrolizumab as first-line therapy —23 percent  saw tumors shrink by more than 30 percent, while the disease was stabilized in 9 of them, or 17 percent. We do not yet have survival data or Group B.

These results to immunotherapy as a drug with activity against metastatic triple negative breast cancer. Intriguingly, the drug appears active whether the target PD-L1 is present or not. These data do not represent a home run, but suggest promise for the treatment of a very aggressive form of breast cancer that currently has limited options for treatment. The side effects seemed reasonable, with severe toxicity among 12 percent of those in group A, and 8 percent in group B. The most common side effects were fatigue and nausea. In addition, there are some hints that the drug is more effective when given earlier in the course of management for metastatic breast cancer. The bottom line? A small subset of patients will respond to immunotherapy, but if one does respond, the disease control can be durable. I’m Dr. Michael Hunter.

Dr. Michael Hunter