Shares of Exelixis (NASDAQ:EXEL) got hit hard last week after the company said its clinical trial testing Cometriq in prostate cancer would continue. While the continuation of a trial would normally be a non-event -- we'll get the final data before the end of the year -- investors were clearly hoping that the drug would work so well that the trial would be stopped early.

While the trial could still prove successful on the final look at the data, some of the stock price decline is warranted because how well Cometriq works will ultimately determine how well the drug competes against Johnson & Johnson's (NYSE:JNJ) Zytiga and Medivation (NASDAQ:MDVN) and Astellas' Xtandi.

In the following video, Fool contributor Brian Orelli and health-care bureau chief Max Macaluso discuss what the news means for Exelixis, Johnson & Johnson, Medivation, and Astellas.