By Anora Mahmudova, MarketWatch

NEW YORK (MarketWatch) -- U.S. stocks rose on Tuesday with the S&P 500 and Nasdaq set for a sixth-straight day of gains.

A flurry of estimate-beating earnings from heavyweights such as Lockheed Martin Corp. (LMT) and Comcast Corp. (CMCSA), as well as deal news in the health-care sector, boosted sentiment.

The sales pace of existing homes ticked down in March to the slowest rate since July 2012, according to data released Tuesday.

The S&P 500 (SPX) rose 12 points, or 0.6%, to 1,883.56, extending its winning streak to the sixth session. The health-care sector is leading gains thanks to deal activity between several pharmaceutical companies, including Allergan and Valeant.

The Dow Jones Industrial Average (DJI) added 100 points, or 0.6%, to 16,546.95.

The Nasdaq Composite (RIXF) rose 45 points, or 1.1%, to 4,166.77, helped by a 6% rally in Netflix, Inc. Biotechnology and pharmaceutical companies also rallied.

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Comcast, Lockheed Martin beat expectations; Allergan jumps

In earnings news, Comcast Corp. (CMCSA) shares climbed 2.9% after the telecommunications company reported first-quarter earnings and revenue ahead of analyst forecasts.

"Earnings have not been stellar, especially on revenue side, but it seems that results are good enough for investors who are in a 'buy the dip' state of mind," said Channing Smith, managing director at Capital Advisors.

"Deals are helping markets, but it is a worrying sign when both acquisition target and acquiring companies rise after announcing a deal," he added.

Lockheed Martin Corp. (LMT) fell 1.9% after the aerospace and defense firm raised its 2014 earnings guidance and posted a rise in first-quarter profit.

Harley-Davidson Inc. rose 7.4% after beating quarterly earnings estimates. The Milwaukee-based maker of motorcycles reported a 19% rise in first-quarter profit, despite an uptick in loan losses at the company's financing unit.

Netflix, Inc (NFLX) shares rallied 5.9% after the video-streaming company beat expectations for the first-quarter results.

McDonald's Corp. (MCD) shares were down 0.7% even as the company's first-quarter results missed expectations. Earnings for the first three months of the year fell, dragged by a decline in sales in the U.S. amid fierce competition and consumers' growing appetite for healthier foods.

Xerox Corp. (XRX) shares were up 2.1% after reporting a fall in the first-quarter earnings as revenues continued to shrink. The company trimmed its full-year adjusted earnings expectations.

In deal news, shares of Allergan Inc. (AGN) surged 16% after Valeant Pharmaceuticals International Inc. (VRX) and activist investor Bill Ackman joined forces and proposed a buyout of Allergan. Valeant shares rose 7.7%.

After the closing bell, more companies are scheduled to report earnings, including, AT&T (T) -- expected to report earnings of 70 cents a share in the first quarter, and Yum Brands (YUM) -- forecast to post earnings of 84 cents a share in the first quarter. Yum Brands was downgraded to neutral from overweight at J.P. Morgan on Monday.

In other financial markets, European stock indexes posted solid gains on their first trading day after the Easter break amid increasing deal activity in the pharma sector. Asian bourses closed mixed. Meanwhile, oil declined and most metals prices moved higher.

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