US STOCKS-Wall St ends flat as recent rally spurs caution
* Investors uncertain about valuation
* Starwood up after Marriott's higher offer
* IHS up after deal to buy Markit
* Valeant rises on search for new CEO; Ackman to join board
* Dow up 0.12 pct, S&P up 0.1 pct, Nasdaq up 0.28 pct (Updates to close)
By Laila Kearney
New York, March 21 (Reuters) - Wall Street closed little changed on Monday as investors searched for fresh catalysts and showed concerns about fully-extended share prices after a five-week rally.
The session, which closed slightly higher and opened slightly lower, followed a market-friendly move by the U.S. Federal Reserve last week that pushed the S&P 500 and Dow into positive territory for the year.
"I think people are starting to become concerned about valuation here," said Stephen Massocca, chief investment officer at Wedbush Equity Management in San Francisco. "Given the rally that we've had over last few weeks, stocks are extended and susceptible to bad news." Continuación...