US regulators have agreed to undertake a priority review of Merck's application to market its immunotherapy Keytruda for the first-line treatment of patients with advanced non-small cell lung cancer (NSCLC) whose tumours express PD-L1.

The submissions contain data from the pivotal Phase III KEYNOTE-024 study, which showed that Keytruda (pembrolizumab) monotherapy resulted in superior progression-free survival (PFS) as well as overall survival (OS) compared with standard chemotherapy in patients with advanced NSCLC whose tumours expressed high levels of PD-L1.

The trial was stopped early on the back of these results to give patients still on chemotherapy the opportunity to receive treatment with the drug.

"Chemotherapy has been the foundation of first-line treatment for non-small cell lung cancer for decades, so the significant improvement in survival in patients with high PD-L1 expression seen with Keytruda compared to chemotherapy is welcome news," said Dr Roger M. Perlmutter, president, Merck Research Laboratories.

The US Food and Drug Administration also assigned the drug Breakthrough Therapy Designation, intended to expedite the availability of promising new therapies that target a serious or life-threatening condition when early clinical evidence indicates substantial improvement over existing therapies.

Keytruda also carries breakthrough status for specific patients with advanced melanoma, metastatic NSCLC in previously treated patients, microsatellite instability high metastatic colorectal cancer, and relapsed or refractory classical Hodgkin Lymphoma.

The drug is already available in the US to treat patients with metastatic NSCLC whose tumours express PD-L1 with disease progression on or after platinum-containing chemotherapy, having been given an accelerated approval based on tumour response rate and durability of response.

An sBLA is currently under review with the FDA for full approval of the existing second-line NSCLC indication, based on data from KEYNOTE-010, a pivotal phase II/III confirmatory trial which demonstrated improved survival with Keytruda compared to standard chemotherapy in the patient group. A decision is expected by October 24 this year.