U.S. stocks extended declines on Thursday, with the Nasdaq briefly dropping 1 percent, weighed down by declines in biotech companies such as Celgene Corp and Gilead Sciences Inc .

* The Dow Jones industrial average <.DJI> dropped 38.24 points, or 0.41 percent, to 9,242.73. The Standard & Poor's 500 Index <.SPX> dropped 5.95 points, or 0.59 percent, to 996.77. The Nasdaq Composite Index <.IXIC> dropped 16.52 points, or 0.83 percent, to 1,976.53.

(Reporting by Chuck Mikolajczak; Editing by Padraic Cassidy)