US STOCKS-Wall St rises on Yellen's view; S&P scores modest Q1 gain
* S&P 500 rises in Q1 for its fifth straight quarterly gain
* Gains broad, materials and tech outperform
* Yellen says easy Fed policies needed for some time
* Prana Biotech sinks on results of Alzheimer's drug study
* Dow up 0.8 pct; S&P 500 up 0.8 pct; Nasdaq up 1 pct (Updates to close)
By Ryan Vlastelica
NEW YORK, March 31 (Reuters) - U.S. stocks rose on Monday, with the S&P 500 ending both March and the first quarter of 2014 with moderate gains, after Federal Reserve Chair Janet Yellen relieved concerns about a rate hike coming earlier than expected.
This was the fifth straight quarterly rise for both the S&P 500 and the Nasdaq, though it was the smallest three-month advance for both since the fourth quarter of 2012. Both the Dow and the S&P 500 rose for a second straight month in March.
Gains were broad, with nine of the S&P 500's 10 sector indexes rising for the day. About 73 percent of stocks traded on both the New York Stock Exchange and the Nasdaq closed higher. Continuación...