The Nasdaq was down 0.76% to 3,156 in midday trading Monday, while the Dow Jones Industrial Average fell 0.21% to 13,550.
The S&P 500 was off 0.33% to 1,455.
The yield on a 10-year treasury bond fell 2.67% to 1.71%.
The price of gold was off 0.66% to $1,766 per ounce.
Shares of Anaheim-based drug maker Questcor Pharmaceuticals Inc. fell about 32% to $20 after the company said in a filing with the Securities and Exchange Commission that it is being investigated by the U.S. government on promotional practices for its flagship drug. Questcor's shares plunged about 48% Sept. 19 after an online newsletter reported that insurer Aetna Inc. would limit coverage of Questcor's only drug Acthar Gel. The stock rebounded slightly the following day when Questcor Chief Executive Don Bailey said Aetna's decision would not negatively impact the business.
Questcor has a market value of about $1 billion.
Tustin-based Peregrine Pharmaceuticals Inc.’s shares slumped 76% to $1.30 after the drug developer reported discrepancies in the results of its leading product and lung cancer treatment bavituximab. Peregrine has a market value of about $126 million.
Identive Group Inc. shares were up about 10% to $0.78 for a market value of $47 million. The Santa Ana-based company makes scanners, readers and other devices used for security on buildings and computers.