Roche Holding AG said on Wednesday it is buying privately held U.S. biotech firm Seragon Pharmaceuticals for up to $1.725 billion. Under the agreement, Genentech -- part of Roche Group -- will pay $725 million upfront in cash, plus up to an additional $1 billion based on performance of "certain predetermined milestones." The transaction is expected to close in the third quarter of 2014. Seragon researches breast-cancer treatment.

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