Infusion of pembrolizumab (MK-3475) produced durable responses in almost one out of five patients with metastatic triple-negative breast cancer. The disease has no approved targeted therapies.
The multi-center, non-randomized phase-Ib clinical trial was designed to evaluate the safety, tolerability and antitumor activity of bi-weekly infusions of pembrolizumab. 27 patients, aged 29-72 years, with metastatic triple-negative breast cancer that had either relapsed after treatment for early stage disease or progressed on therapy for advanced disease, were part of the trial.
The metastatic triple-negative tumors have high levels of a protein called programmed death-ligand 1 (PD-L1), which can suppress the immune system's efforts to eliminate cancer cells. Pembrolizumab, a monoclonal antibody, is designed to help reactivate a person's own immune system to help fight the tumor.
Study director Rita Nanda, MD, assistant professor of medicine and associate director of the breast medical oncology program at the University of Chicago, said, "Of the 27 patients in this study with measurable disease, five (18.5%) had encouraging results. One patient had a complete response, and four had a partial response to treatment."
Pembrolizumab was approved by the Food and Drug Administration for treatment of melanoma in September 2014. It has side-effects like fatigue, cough, nausea, itchy skin, rash, decreased appetite, constipation, joint pain and diarrhea; which are generally mild and easy to tackle. During the trial 4 of the 27 patients experienced at least one severe or life-threatening drug-related adverse event. One patient died while on the study treatment.
An earlier study of pembrolizumab by Dr. Tanguy Seiwert, MD, assistant professor of medicine at the University of Chicago, found a similar response rate in PD-L1 positive patients with advanced head and neck cancer.
The median survival for patients with triple-negative breast cancer is approximately a year and better treatments are needed to manage the disease. The promising activity of pembrolizumab is certainly worthy of further investigation. Researchers are looking forward to learn how to predict which patients are most likely to benefit and how to manage the drug's toxicity.