SPDR S&P Biotech ETF ( XBI) -1.7% For a second day, biotechnology stocks are heading lower, pushing ETFs like XBI and the iShares NASDAQ Biotechnology Index Fund ( IBB) to the top of the loser's list. At the start of the week, I warned investors that these funds could be set to take a breather given their impressive run ups during the opening weeks of the year. Continue to keep them on the radar. All prices as of 2:12 PM EST. Written by Don Dion in Williamstown, Mass.