The FDA today granted accelerated approval for Keytruda (pembrolizumab, Merck & Co) to treat patients with advanced (metastatic) non-small cell lung cancer (NSCLC) whose disease has progressed after other treatments and with tumors that express a protein called PD-L1, according to an agency news release.

The drug is approved for use with a companion diagnostic, the PD-L1 IHC 22C3 pharmDx test (Dako North America), the first test designed to detect PD-L1 expression in non-small cell lung tumors. In 2014, Keytruda was approved to treat patients with advanced melanoma following treatment with ipilimumab, a type of immunotherapy.

According to the FDA, Keytruda works by targeting the cellular pathway known as PD-1/PD-L1 (proteins found on the body’s immune cells and some cancer cells). By blocking this pathway, Keytruda may help the body’s immune system fight the cancer cells.

Keytruda was approved under the agency’s accelerated approval program, which allows the approval of a drug to treat a serious or life-threatening disease based on clinical data showing the drug has an effect on a surrogate endpoint reasonably likely to predict clinical benefit to patients. This program provides earlier patient access to promising new drugs while the company conducts confirmatory clinical trials. An improvement in survival or disease-related symptoms in patients being treated with Keytruda has not yet been established.

“Our growing understanding of underlying molecular pathways and how our immune system interacts with cancer is leading to important advances in medicine,” said Richard Pazdur, MD, director of the Office of Hematology and Oncology Products in the FDA’s Center for Drug Evaluation and Research. “Today’s approval of Keytruda gives physicians the ability to target specific patients who may be most likely to benefit from this drug.”

The safety of Keytruda was studied in 550 patients with advanced NSCLC. The most common side effects of Keytruda included fatigue, decreased appetite, shortness of breath or impaired breathing (dyspnea) and cough. Keytruda also has the potential to cause severe side effects that result from the immune system effect of Keytruda (known as “immune-mediated side effects”).

Read more about Keytruda at the FDA’s website.