In just two days, Exelixis (NASDAQ:EXEL) has lost over 15% of its market cap. The tumble for the once-hot biotech stock started last week with a downgrade of the stock by an analyst at Leerink Partners. It wasn’t over anything Exelixis did -- analyst Mike Schmidt said the biotech’s fundamentals still appear to be strong. Instead, the concerns were about Exelixis stock’s valuation.
