An antitrust suit filed on behalf of a class of end payors alleges Celgene Corp. took steps to prevent the approval of generic versions of its cancer drugs Thalomid and Revlimid.

Celgene charges up to $500 per capsule for the drugs, and has taken in $17.1 billion selling them from 2009 to 2013, the suit says. The company has unlawfully perpetuated a monopoly by interfering with efforts to develop generic versions, according to the suit. The plaintiff, the city of Providence, Rhode Island, brought the suit on behalf of users and end payors of the drugs.