Johnson & Johnson's Zytiga Scores Big Win, Hurts Dendreon Corporation, Helps Medivation, Inc.

Johnson & Johnson's(JNJ_) prostate cancer drug Zytiga prolonged the lives of patients with less advanced disease, according to results of a late-stage study announced Thursday. Zytiga, a pill, is now in line to treat the same prostate cancer patients targeted by Dendreon(DNDN_) with its Provenge immunotherapy. Dendreon shares fell $1.28 or 12% to $9.64 in Thursday's pre-market on fears that Zytiga competition may further erode already-underperforming Provenge sales. Meantime, Medivation(MDVN_) shares jumped $9.61 or 15% to $73.80 because its prostate cancer drug MDV3100 is a close cousin to Zytiga. Medivation is also conducting a late-stage study of MDV3100 in the same population of prostate cancer patients.