Wall Street is drifting between gains and losses Thursday as UnitedHealth Group’s stock plunges toward its worst drop in more than a quarter century, while most of the rest of the U.S. stock market ticks higher.

U.S. stock indexes were mixed in choppy trading on Thursday as investors weighed progress in trade negotiations with Japan against concerns about the monetary policy outlook, while a slump in UnitedHealth's shares weighed on the Dow.

Most U.S. stocks rose, but the worst drop for UnitedHealth Group in a quarter century kept Wall Street in check.