US STOCKS-Wall St ends lower as Caterpillar, health stocks weigh
* Caterpillar hits 5-year low after sales forecast cut
* Health stocks see 5th day of losses, biotech index falls 2 pct
* Investors await Yellen speech at 5 p.m. ET
* Indexes down: Dow 0.48 pct, S&P 0.34 pct; Nasdaq 0.38 pct (Updates to close, adds commentary)
By Sinead Carew
Sept 24 (Reuters) - U.S. stocks closed lower on Thursday in a volatile session on uncertainty about U.S. monetary policy and global economic growth, while market heavyweight Caterpillar cut in its sales forecast and healthcare investors fled for the exits.
Six of the 10 major S&P sectors were lower, with the health sector's 1-percent fall leading the S&P declines and the Nasdaq biotech sector down 2 percent. Both healthcare indexes had their fifth straight day of losses.
While the broader market pared losses somewhat in the afternoon, investors were cautious ahead of a speech by Federal Reserve Chair Janet Yellen, which could provide clues regarding the timing of an increase in U.S. interest rates.
Yellen, due to deliver an inflation speech at 5 p.m. ET (2100 GMT), had cited concerns about slowing global growth as a key reason for holding off from a long-anticipated Fed rate hike last Thursday. Continuación...