US STOCKS-S&P 500 and Nasdaq gain, but investors cautious
* AstraZeneca rejects sweetened Pfizer offer
* AT&T to buy DirecTV for $48.5 billion
* Dow off 0.01 pct; S&P 500 up 0.3 pct; Nasdaq up 0.7 pct (Updates to midday)
By Chuck Mikolajczak
NEW YORK, May 19 (Reuters) - U.S. stocks mostly advanced on Monday as investors exercised caution over valuations after a run of mixed economic data, but another drop in bond yields helped support equities.
U.S.-listed shares of AstraZeneca tumbled 11.1 percent to $71.39. The British drugmaker rejected a sweetened and final merger offer from Pfizer that would have created the world's largest pharmaceuticals group. Pfizer shares climbed 1.1 percent to $29.45.
AT&T slid 1.9 percent to $36.03 and dragged on the Dow a day after the telecom company said it will acquire DirecTV for $48.5 billion, as it seeks fresh avenues of growth beyond the maturing U.S. cellular business. DirecTV shares fell 1.4 percent to $84.92.
Equities have come under pressure recently with the S&P 500 marking consecutive weekly declines for the first time since January as investors have become concerned about the U.S. economy's growth prospects. Last week, readings on retail sales and consumer sentiment fell shy of expectations while labor and housing data provided reason for optimism.
But with the yield on the 10-year U.S. Treasury note at 2.5 percent, investors may have been compelled to wade into equities and help keep them afloat. Continuación...