WASHINGTON (AP) - Federal health officials have expanded approval of an innovative Merck drug to treat patients with an advanced form of the most common lung cancer.

WASHINGTON (AP) Federal health officials have expanded approval of an innovative Merck drug to treat patients with an advanced form of the most common lung cancer.

The Food and Drug Administration approved Keytruda for advanced non-small cell lung cancer patients who have not responded to other therapies. The disease accounts for roughly seven out of eight cases of lung cancer in the U.S.

Keytruda is part of a promising new class of drugs called immunotherapies, which harness the body's immune system to help fight cancer. The company's injectable biotech drug works by blocking a protein found in certain tumors called PD-1, which inhibits the body's natural response against cancer cells.

Bristol-Myers Squibb won FDA approval for a similar indication for its own PD-1 drug, Opdivo, in March.