(Reuters) – Bristol-Myers Squibb Co said on Friday the U.S. Food and Drug Administration approved its treatment, Opdivo, for patients whose lung cancer had progressed even after undergoing chemotherapy and at least one other therapy.

The drug competes with Merck & Co’s Keytruda and belongs to a class of treatments that work by activating the immune system to attack tumors.

Both treatments have racked up approvals for indications, including melanoma, lung cancer and head and neck cancer.

Sales of both the drugs are neck and neck, with Opdivo generating $1.63 billion in the second quarter and Keytruda $1.67 billion.

Bristol-Myers said Opdivo is the first immunooncology treatment approved for patients with small cell lung cancer, which accounts for about 10 to 15 percent of all lung cancers.

Bristol-Myers shares rose 0.5 percent to $61.40 in premarket trading.

(Reporting by Aakash Jagadeesh Babu and Ashwin Shyam in Bengaluru; Editing by Anil D’Silva)