ZURICH (Reuters) – Roche said on Thursday the U.S. Food and Drug Administration (FDA) had extended by three months the review period for Tecentriq in combination therapy as a first-line treatment for a form of lung cancer.

The news is a sign that U.S. approval of the Swiss drugmaker’s immunotherapy may not go as smoothly as hoped.

Roche is hoping to clinch more of the lung cancer treatment market with its Tecentriq immunotherapy, but suffered a setback in July when a trial failed to deliver survival data it needs to challenge rival Merck.

“The extension allows the FDA time to review additional information requested in support of the supplemental Biologics License Application”, Roche said in a statement.

It said the FDA was expected to make a decision on the approval by Dec. 5.

Tecentriq — also known as atezolizumab — in combination with Avastin, carboplatin and paclitaxel was granted priority review from the FDA in May for the initial treatment of people with metastatic non-squamous non-small cell lung cancer (NSCLC).

It is already approved in the European Union, United States and more than 70 countries for people with previously treated metastatic NSCLC and for certain types of untreated or previously treated metastatic urothelial carcinoma.

Roche said in a separate release on Thursday that it would present new data from its Tecentriq lung cancer program at a conference this month.

Roche shares were set to open 0.7 percent lower, according to pre-market indications by bank Julius Baer.

(Reporting by Silke Koltrowitz; Editing by Maria Sheahan and Michael Shields)