21st Century Oncology Inc., a cancer treatment giant, filed for bankruptcy Thursday after reaching an agreement with lenders and bondholders that would prune more than half a billion dollars in debt from the company’s balance sheet.

The cancer care provider and its affiliates sought chapter 11 protection at the U.S. Bankruptcy Court in White Plains, N.Y., with total assets and liabilities each topping $1 billion. The company emphasized Thursday it will remain open and continue patient treatment uninterrupted while in bankruptcy.

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