On May 23, the US Food and Drug Administration (FDA) granted accelerated approval to pembrolizumab, made by Merck and marketed as Keytruda, for adults and children without remaining treatment alternatives and with metastatic solid tumours identified with a biomarker called microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR).
Tumours with MSI-H and dMMR markers – most commonly found in colorectal, endometrial, and gastrointestinal cancers – have abnormalities that affect DNA repair inside the cell. It’s believed that Keytruda works by blocking a cellular pathway known as PD-1/PD-L1, containing proteins found on the body’s immune cells and some cancer cells. According to a report by Quartz Media, the drug “may help the body’s immune system fight the cancer cells” but the FDA doesn’t specify how.
In clinical trials, pembrolizumab showed promise in treating cancers originating in 15 different locations. The FDA decision is based on a study of 90 patients with colorectal cancer and 59 patients with one of 14 other cancer types. Of these 149 patients, 39% had a complete or partial shrinkage of tumours, which for 79% of patients lasted for six months or more.
“This is an important first for the cancer community,” said Richard Pazdur, MD, acting director of the Office of Hematology and Oncology Products in the FDA’s Centre for Drug Evaluation and Research and director of the FDA’s Oncology Centre of Excellence. “Until now, the FDA has approved cancer treatments based on where in the body the cancer started — for example, lung or breast cancers. We have now approved a drug based on a tumour’s biomarker without regard to the tumour’s original location.”
More research needs to be done although the drug has already been approved for certain specific cancer treatments – metastatic melanoma, metastatic non-small cell lung cancer, recurrent or metastatic head and neck cancer, refractory classical Hodgkin lymphoma and urothelial carcinoma.