US STOCKS-Wall St falls as Caterpillar, health stocks weigh
* Caterpillar hits 5-year low after sales forecast cut
* Health stocks on track for 5th day of losses
* Investors await Yellen speech at 5 p.m. ET
* Indexes down: Dow 0.64 pct, S&P 0.54 pct; Nasdaq 0.72 pct (Updates to late afternoon, adds commentary)
By Sinead Carew
Sept 24 (Reuters) - Key U.S. stock indexes fell in afternoon trading on Thursday, weighed by tumbling healthcare stocks and shares of market heavyweight Caterpillar after a cut in its sales forecast added to worries over sluggish global growth.
Eight of the 10 major S&P sectors were lower, with the health sector's 1.4 percent fall leading the declines. The Nasdaq biotech sector was down 2.8 percent. Both indexes were on track for a fifth straight day of losses.
While the market pared losses somewhat in late afternoon trading, 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.
"You need to see better China data and more certainty about the Fed," said Scott Wren, senior global equity strategist at Wells Fargo Investment Institute in St. Louis, Missouri. Continuación...