"Well-known biotech "frequent flyers" like MannKind (MNKD), Hemispherx (HEB), and XOMA (XOMA) have all come to life again over the past six months or so. Likewise, a host of investors seem to be happy playing in low-quality names popular with retail investors on the idea that bullish press releases can continue to fire the stocks."

http://seekingalpha.com/article/897731-is-biotech-getting-too-frothy-investor-sentiment-suggests-irrational-exuberance