Biotech is getting roughed up, after leading the market's gains this year.
The iShares Nasdaq Biotechnology ETF, IBB, tumbled more than 4 percent, as bad news hit a couple of companies in the sector. The IBB, however, is still 15 percent higher year to date and held a low just above its 50-day moving average at 347.77. The larger-cap S&P health-care sector has the led the market year to date, and it was down 1.4 percent. It is up 7 percent for the year.
Celladon led the biotech group's decline with a dramatic 80 percent drop. The company, which went public last year, plunged after its heart failure gene therapy, Mydicar, failed to meet goals in an important study.
Read MoreStocks mostly lower, as biotech lags