Profit at Regal Entertainment Group, the nation's biggest theater owner, plunged to $4 million from $13.6 million last quarter in what CEO Amy Miles called ''a challenging box office environment.''

Revenue at the Knoxville, Tenn.-based chain fell to $614 million from $661 million.

Operating costs were down, however. And Miles in a statement noted the company's successful completion of 3D projector deployment and the launch of Open Road Films. She also said she's ''encouraged by the early 2012 box office results and the line-up of films slated for the upcoming summer season.''

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