Bristol-Myers Squibb and Ono Pharma sue Merck over Keytruda

US drug major Bristol-Myers Squibb (NYSE: BMY) and partner Japan’s Ono Pharmaceutical (TYO: 4528) have filed a law suit against pharma giant Merck & Co (NYSE: MRK) over Keytruda (pembrolizumab) for advanced melanoma.

The companies maintain that the drug is in breach of their patent covering immunotherapy techniques. The drug is the first of a new class of cancer drugs that uses the body's immune system to fight tumors, inhibiting the action of PD-1 and blocking a major pathway by which cancer cells evade the immune system.

The law suit was filed in the Federal Court of Delaware on Thursday, the same day the drug was granted accelerated approval by the US Food and Drug Administration, making it the first FDA-cleared anti-PD-1 therapy. This cleared the way for a US launch and a scramble for dominance in a field expected to peak at nearly $35 billion a year.