* Yellen says central bank commitment needed for some time
* Prana Biotech tumbles after Alzheimer's drug study results
* Chicago PMI hits lowest level since August
* Indexes up: Dow 0.85 pct, S&P 0.82 pct, Nasdaq 1.16 pct (Updates to open, adds quote, data, Yellen comments)
By Chuck Mikolajczak
NEW YORK, March 31 (Reuters) - U.S. stocks rose on Monday, putting the S&P 500 on track for a second straight advance, led by technology and financial shares following comments from Federal Reserve Chair Janet Yellen.
Each of the 10 major S&P indexes was in positive territory, led by technology, up 1.1 percent, and financials , up 1 percent. Microsoft Corp gained 2.3 percent to $41.22 and JPMorgan Chase & Co rose 1.5 percent to $60.96 as the two biggest boosts to the S&P 500.
Yellen said the U.S. central bank's "extraordinary" commitment to boosting the economy, especially the still struggling labor market, will be needed for some time to come.
"I don't think she is going to be pull back on the taper, she is just being realistic in recognizing the fact things are still slow, but they are going to continue down the path," said Ken Polcari, Director of the NYSE floor division at O'Neil Securities in New York.
Equities also received a boost from end-of-quarter "window dressing," when money managers adjust their positions to improve the look of their portfolios.
"It's absolutely the end of the quarter, last day of the month, trying to close it at the high - so it's a big push just to try and keep it at least flat to slightly positive (for the quarter)," said Polcari.
With Monday's advance, the S&P 500 is up 0.7 percent for the month and up 1.3 percent for the quarter, which would mark the worst quarterly performance for the benchmark index since the last quarter of 2012.
The Dow Jones industrial average rose 138.42 points, or 0.85 percent, to 16,461.48, the S&P 500 gained 15.29 points, or 0.82 percent, to 1,872.91 and the Nasdaq Composite added 48.372 points, or 1.16 percent, to 4,204.13.
The Institute for Supply Management-Chicago business barometer was at 55.9 in March, its lowest level since August and down from 59.8 in February. Economists' median forecast in a Reuters poll was 59.0.
U.S.-listed shares of Prana Biotechnology Ltd plunged 70.9 percent to $2.87 after the company said its experimental drug to treat Alzheimer's disease failed to meet the main goal of a mid-stage study in patients with a mild form of the condition.
Many biotechnology stocks have come under pressure recently, and the Nasdaq Biotechnology index fell 7 percent last week, its fifth consecutive week of declines.
Logistics company UTi Worldwide Inc reported a bigger-than-expected quarterly loss, hurt by weak demand for air freight as customers opted for cheaper modes of shipping. Its shares slumped 8.6 percent to $10.29.
Editing by Bernadette Baum