US regulators have issued a green light for first-line use of Merck's immunotherapy Keytruda to treat patients with certain forms of lung cancer.

The US Food and Drug Administration has cleared the drug's use in untreated patients with metastatic non-small cell lung cancer (NSCLC) whose tumours have high PD-L1 expression as determined by an FDA-approved test, with no EGFR or ALK genomic tumour aberrations.

The decision, which makes Keytruda (pembrolizumab) the only anti-PD-1 therapy to be cleared in the first-line setting for these patients, came on the back of data from the pivotal Phase III KEYNOTE-024 study.

This showed that Keytruda monotherapy resulted in superior progression-free survival and overall survival compared with standard chemotherapy in patients with advanced NSCLC whose tumours expressed high levels of PD-L1; reducing the risk of progression by 50 percent and the risk of death by 40 percent.

Roger Perlmutter, president of Merck Research Laboratories, said first-line approval of the drug "has the potential to change the treatment landscape for these patients."

"Patients now have an option beyond chemotherapy at initial diagnosis. This approval reinforces the need for biomarker testing so care can be personalised and most effective," added Laurie Fenton Ambrose, president and chief executive of the Lung Cancer Alliance.

Keytruda is a humanised monoclonal antibody that works by increasing the ability of the body's immune system to help detect and fight tumour cells, by blocking the interaction between PD-1 and its ligands to activate T lymphocytes.

In the US, the drug is already on the market to treat metastatic NSCLC, melanoma and head and neck cancer.