(Updates close with jump in Agenus; adds Gogo's shares down after the bell)
* Pfizer works on next move in takeover bid for Astrazeneca
* Amazon.com leads Nasdaq's loss
* Bank of America drops after suspending dividend increase, buyback plan
* Dow up 0.5 pct; S&P 500 up 0.3 pct; Nasdaq down 0.03 pct
By Caroline Valetkevitch
NEW YORK, April 28 (Reuters) - The S&P 500 ended higher on Monday after a volatile session, as gains in Apple and Pfizer helped offset another round of selling in some high-growth tech shares.
The Dow also managed to end the session with a modest gain, while the Nasdaq closed slightly lower after rebounding from a fall of over 1 percent. Leading the Nasdaq down was Amazon.com , which extended Friday's sharp drop a day after its earnings report.
A flurry of merger and acquisition activity in the pharmaceutical sector increased speculation of further deal-making. Shares of Pfizer gained 4.2 percent to $32.04 after the U.S. drugmaker was said to be working on its next move in a potential bid to take over Britain's AstraZeneca Plc.
"What we saw earlier was you had more rotation out of the high-beta momentum names, and a lot of those tech players rotated into Apple, which just had positive earnings," said Michael O'Rourke, chief market strategist at JonesTrading in Greenwich, Connecticut.
"This whole M&A aspect of the pharmaceutical healthcare industry has people positively biased for the time being," he said, and "people who had to sell the momentum names are at least finished for the time being."
The Dow Jones industrial average rose 87.28 points or 0.53 percent, to end at 16,448.74. The S&P 500 gained 6.03 points or 0.32 percent, to 1,869.43. The Nasdaq Composite dropped 1.161 points or 0.03 percent, to 4,074.401.
Apple's stock jumped 3.9 percent to $594.09. The stock has gained 13.2 percent since the close on Wednesday, when Apple reported results after the bell.
Amazon.com ended down 2.4 percent at $296.58. High-growth stocks have been battered in recent weeks as investors have pulled out of the tech and biotech space.
Bank of America shares tumbled 6.3 percent to $14.95 after the company said it will suspend a planned increase in its quarterly dividend as well as its latest stock-buyback program because it miscalculated a measure of the capital on its books.
Chinese Internet stocks also fell after China's government ordered the removal of four U.S. television shows from video websites. The U.S.-listed shares of Baidu slid 7.4 percent to $150.93.
In other M&A activity, Forest Laboratories Inc said it would buy Furiex Pharmaceuticals Inc for up to $1.46 billion. Furiex Pharmaceuticals shares surged 28.6 percent to $103.05 while Forest Laboratories shares shed 0.4 percent to $89.50.
Agenus shares jumped 19.5 percent to $3.06 after the biotechnology company said it signed a deal with Merck & Co Inc to discover and develop antibody-based treatments against cancer.
After the bell, shares of in-flight wireless Internet services provider Gogo dropped 19.2 percent to $14.85 after AT&T said it plans to launch an in-flight connectivity service.
During the session, about 7.4 billion shares changed hands on U.S. exchanges, above the 6.5 billion average so far this month, according to data from BATS Global Markets.
(Editing by Bernadette Baum and Jan Paschal)