The US Food and Drug Administration (FDA) has approved Merck’s anti programmed cell death protein 1 (PD-1) therapy Keytruda as a monotherapy to treat metastatic small cell lung cancer (SCLC) patients.

Merck Research Laboratories oncology clinical research vice-president Dr Jonathan Cheng said: “Keytruda is already an established treatment option for non-small cell lung cancer, and today’s approval in small cell lung cancer demonstrates our commitment to bringing forward new treatment options for patients with advanced, difficult-to-treat cancers.

“We look forward to continuing to advance important clinical research in small cell lung cancer.”

The FDA’s accelerated approval was based on the drug’s tumour response rate and durability of response in two multi-centre, multi-cohort, non-randomised, open-label clinical trials.

Called Keynote-158 (cohort G) and Keynote-028 (cohort C1), patients with autoimmune disease or a medical condition that required immunosuppression were not considered for the trials.

A total of 83 patients were enrolled to be evaluated for efficacy. Of the total participants, 64% received two prior lines of therapy and 36% were given three or more lines.

Another 60% of the subjects received prior thoracic radiation therapy, while 51% received prior radiation therapy.

The humanised monoclonal antibody (mAb) Keytruda is capable of increasing the ability of the body’s immune system and helps to detect and fight tumour cells. It blocks the interaction between PD-1 and its ligands, PD-L1 and PD-L2. It then activates T lymphocytes, which may affect both tumourous and healthy cells.

Merck is currently carrying out more than 1,000 trials of Keytruda across a range of cancers and treatment settings.