A steep slide in UnitedHealth Group Inc. shares dragged on the Dow Jones Industrial Average on Thursday, leaving the blue-chip index with historical underperformance versus the S&P 500.

On Thursday, the Dow Jones Industrial Average became the latest major U.S. equity-market gauge to experience a “death cross.” It was the first time the ominous signal has appeared on the price ...

The Dow Jones Industrial Average tumbled 527 points, or 1.3%, to 39,142.23. The S&P 500 rose 0.1%, and the Nasdaq edged down 0.1%. The Dow tumbled more than 500 points, or 1.3% on Thursday.