(Adds information about possible spinoff of MSG business, updates stock price.)

Cablevision Systems Corp. (CVC) swung to a first-quarter profit, helped by strong results at its telecommunications-services business, and said it will explore a spinoff of its Madison Square Garden business.

Shares jumped 12% to $20.47.

Looking at a possible spinoff for MSG, which includes the New York Knicks and Rangers, comes after Chief Executive James Dolan said in February there was "no change" in the company's plans to spend $500 million renovating the iconic arena.

Meanwhile, Cablevision reported a profit of $20.2 million, or 7 cents a share, reversing a year-earlier loss of $31.6 million, or 11 cents a share. The loss on derivative contracts narrowed to $33.7 million from $106.3 million.

Revenue rose 11% to $1.9 billion.

Analysts polled by Thomson Reuters expected earnings of 15 cents a share on revenue of $1.9 billion.

At Cablevision's telecommunications business, by far the company's largest, revenue rose 5.3% and earnings jumped 14%, driven by broadband-subscriber growth and higher rates. In February, Chief Operating Officer Thomas Rutledge said cable-subscriber growth in the quarter to that point was ahead of last year's results.

MSG revenue rose 2.3% as its operating loss narrowed sharply amid a prior-year write-down. The company's Rainbow unit - which includes cable channels such as AMC and IFC - posted an 11% revenue rise while operating income rose 40%. Cable networks have been a rare bright spot in the media industry as they are less advertising-dependent.

-By Mike Barris, Dow Jones Newswires; 201-938-5658; mike.barris@dowjones.com