LONDON (Reuters) – Merck & Co’s key cancer drug Keytruda has been approved for use in Europe in combination with chemotherapy in previously untreated lung cancer patients, marking a further advance for the product after uncertainty about its EU prospects a year ago.

Keytruda is the first such immunotherapy medicine to be approved in Europe for first-line use with chemotherapy in patients with advanced non-squamous non-small cell lung cancer, the most common form of the disease.

Lung cancer is by far the most lucrative oncology market with first-line approval providing access to the most patients.

Merck said on Monday that the green light from the European Commission allowed marketing of the combination in all 28 European Union (EU) member states plus Iceland, Lichtenstein and Norway.

The Keytruda/chemo combination is already approved in the United States. But last October the U.S. drugmaker withdrew an application for European approval, casting doubt over its prospects in the region.

Since then, however, the company has produced further clinical data showing the benefits of the combination.

Keytruda has taken a leading position among immunotherapies for the treatment of lung cancer, ahead of rival drugs from Bristol-Myers Squibb, Roche and AstraZeneca.

(Reporting by Ben Hirschler; Editing by Hugh Lawson)