Johnson & Johnson's (JNJ -0.72%) drug Zytiga was just approved in a pre-chemotherapy indication for late-stage metastatic castration-resistant prostate cancer. This came as no surprise to investors; it received approval in Europe recently for a first-line therapy as well. In the following video, Motley Fool health-care analyst David Williamson talks about why this wasn't a big needle-mover for Johnson & Johnson share prices, but he also tells us that it was a critical step forward not only for J&J, which wants to see Zytiga hit the $1 billion mark, but also for Dendreon (NASDAQ: DNDN), which is working on some tandem treatment trials with Zytiga and its pre-chemo immunotherapy drug Provenge, that could prove to be huge share price drivers if successful.