Piper Jaffray's Rating Change Only Had Short-term Impact, Exelixis Down 8.7% (EXEL)

Piper Jaffray upgraded Exelixis (NASDAQ:EXEL) from Neutral to Overweight a week ago. Exelixis stocks closed at $11.51, a 8.7% loss over the course of one week.Exelixis (NASDAQ:EXEL) is currently...