(Reuters) - Johnson & Johnson said on Monday that it would buy Aragon Pharmaceuticals, a private company that is running a mid-stage clinical trial for a prostate cancer drug, for $650 million in cash upfront and a possible second payment of $350 million if it meets certain milestones.

The deal does not include development of Aragon's treatment for breast cancer, which will be spun off into a separate company called Seragon Pharmaceuticals ahead of the deal and will be run by Aragon's chief executive officer.

The acquisition includes Aragon's most advanced drug, called ARN-509, which is currently being evaluated as a treatment for castration-resistant prostate cancer, it said.

(Reporting by Caroline Humer; Editing by Gerald E. McCormick)

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