Bristol Myers Squibb (BMY) and Ono Pharmaceutical have filed a lawsuit against Amgen (AMGN) in Delaware federal court to block a proposed biosimilar of their cancer drug Opdivo.
The suit, filed last week and made public on Monday, alleges that Amgen’s biosimilar candidate would infringe seven U.S. patents covering the blockbuster immunotherapy.
Bristol Myers and Ono are asking the court to block all sales of the Amgen biosimilar while those patents remain in force.
Opdivo, which is also known by its scientific name nivolumab, has been approved in the U.S. to treat advanced or metastatic cancers including melanoma, non-small cell lung cancer, and kidney cancer.
The drug is a significant revenue driver for Bristol Myers, generating more than $5.9 billion in U.S. sales last year alone.
Amgen has already submitted an application to the U.S. Food and Drug Administration seeking approval for its biosimilar version of nivolumab.
An Amgen spokesperson declined to comment directly on the lawsuit but said the company “remains confident” that it will be “in the first wave of Opdivo biosimilars.”
Spokespeople for Bristol Myers and Ono did not immediately respond to requests for comment on the legal action.
The case has been filed as Bristol-Myers Squibb Co. v. Amgen Inc. in the U.S. District Court for the District of Delaware, case number 1:26-cv-01134.
Amgen’s filing represents the first publicly disclosed FDA application for an Opdivo biosimilar, marking a significant moment in the competitive oncology market.
The company has also pointed to an imminent U.S. submission for a biosimilar rival to Merck’s Keytruda, another blockbuster cancer immunotherapy drug, by the end of the year.
Bristol Myers and Ono previously settled a separate patent dispute with Merck in 2017 over Keytruda, with Merck agreeing to pay $625 million plus royalties through 2023.
The legal battle highlights the growing pressure on major branded cancer therapies as biosimilar competition accelerates across the pharmaceutical industry.