The S&P 500 was up 0.2% in midday trading to 2,090.32.
The Dow Jones Industrial Average was up 0.2% to 17,834.77.
The Nasdaq was flat at 5,102.63.
The yield on a 10-year Treasury bond was down 0.2% to 2.25%.
The price of gold was up 0.6% to $1,073.60.
Aliso Viejo-based Microsemi Corp. was down 5.6% to $34.19 and a $3.3 billion market cap. The semiconductor maker agreed to buy PMC-Sierra Inc. in Sunnyvale for $2.5 billion.
Tustin-based Peregrine Pharmaceuticals Inc. was up 5.2% to $1.21 and a $251 million market cap. Shares in the cancer treatment developer had by midday traded at about triple the rate of its 90-day average.
Anaheim-based Pacific Sunwear of California Inc. was up 19% to 35 cents and a $25 million market cap on above-average volume.