M&A news and earnings updates provided some of the catalysts for Monday's most actively traded stocks.
MedImmune shares jumped more than 17% after AstraZeneca agreed to buy the Gaithersburg, Md.-based drugmaker for more than $15 billion. CNBC's David Faber reported last Wednesday that a sale was likely to be announced earlier than expected.
Arch Coalrose as much as 7% after posting solid first-quarter earnings on Monday. Shares of rival coal makers Peabody Energy and Massey Energy were also trading higher.
Carter Worth, chief market technician at Oppenheimer, said coal stocks were in a "bearish-to-bullish reversal" and look to be bottoming. He expects a move of about 10% to 15% for the group over the next several days.
"Arch declined from $56 to $31, and it's no longer declining, it's stabilizing," Worth told CNBC.com. "It looks good, more to come. I would be holding the group."
Steel processing outfit Ryerson saw shares rise 7% on speculation that the Chicago-based company may be acquired by Apollo Management, according to a report by Crain's Chicago Business.
Hasbro , the No. 2 U.S. toymaker, handily beat Wall Street estimates, sending shares up more than 7%. The company said strong sales of Spiderman toys gave a lift to its bottom line.
On the losing side, shares of Applied Micro Circuits fell 22% after the semiconductor company forecast fourth-quarter sales below Wall Street's estimates. Applied Micro said it expects sales to decline 15% sequentially in the first quarter.
Pfizer shares fell after Prudential Equity Group cut its rating on the stock to "neutral" from "buy." Pharmaceutical analyst Tim Anderson said there were only two actions Pfizer could take in order to boost the stock: break up the company or make another major acquisition, neither of which appears likely to happen in the near term.
"While expectations on Pfizer are very low, it is difficult for us to identify tangible sources of upside at the present time," Anderson said.