Biotech and Internet stocks tumbled again Thursday, and the broader market followed.
After a two-day respite, investors again started dumping shares of cutting-edge drug companies and other industries that have soared over the past year. Biotechnology stocks have turned volatile in recent weeks as regulators scrutinize the cost of their drugs and investors worry their earnings won't justify lofty stock prices. Investors are also worried that high-growth companies like Twitter and Facebook have become too expensive.
On Thursday, the Nasdaq composite, which is weighted heavily toward tech and biotech companies, had its worst day since November 2011.