As announced at the annual meeting of the American Association for Cancer Research which met in Philadelphia in April, pembrolizumab either stopped tumor growth or even reversed it in more than three quarters of the mesothelioma patients tested.
Pembrolizumab (brand name Keytruda) is a monoclonal antibody designed to block a cell surface receptor called PD-1. As part of a phase 1B clinical trial known as KEYNOTE-028, researchers at the University of Pennsylvania gave the drug to 25 mesothelioma patients between March and December 2014. These patients all had tumors that tested positive for PD-1 expression. Most had already been through at least one round of pemetrexed-based chemotherapy.
None of the 25 mesothelioma patients treated in the trial had serious drug-related side effects, although 2 patients had to have dose interruptions because of immune-related problems. Just as importantly, none of the patients died as a result of treatment with pembrolizumab.
But the best news is that 76% of mesothelioma patients responded to treatment with pembrolizumab – a figure that the researchers call “unprecedented” among mesothelioma treatment protocols. In 13 of the study participants (52%), their mesothelioma tumors, which had not been stopped by other therapies, temporarily stopped growing. Another six patients actually experienced some level of tumor shrinkage.
“Pembrolizumab is generally well tolerated and provides robust antitumor activity in patients with advanced PD-L positive malignant pleural mesothelioma,” writes Evan Alley, MD, of the University of Pennsylvania’s Abramson Cancer Center in his meeting presentation abstract. “The 76% disease control rate in this previously treated MPM population is unprecedented and warrants further study.”
Pleural mesothelioma, which occurs on the lining around the lungs, is a one of the rarest forms of cancer. It affects approximately 2,500 people in the U.S. each year, most of whom have lived or worked around asbestos. It is highly resistant to conventional cancer therapies and there is no standard second-line treatment for people who are not helped by chemotherapy.
Alley, E et al, “Clinical Safety and efficacy of pembrolizumab in patients with malignant pleural mesothelioma: Preliminary results from KEYNOTE-028”, April 19, 2015, Presentation Abstract, American Association for Cancer Research Annual Meeting 2015. Philadelphia, PA.