So what happens when you and the FDA disagree on the clinical trials needed to show efficacy for your new drug? Well, this happens: your stock opens down 40%. That's what's going on with Exelixis (EXEL) - here are the details. Basically, the company had a fast clinical path in mind, taking its prostate cancer candidate cabozantinib into late-stage patients and using pain reduction as an endpoint. But the FDA wasn't (and isn't) buying that as a marker.
I see their point. Survival is really what you're looking for, and there doesn't seem to be enough evidence that pain reduction is going to translate to that. As that Adam Feuerstein piece notes, all the other prostate drugs have had to show survival benefits. EXEL was planning to follow up with a second trial to show that, but hoped to jump-start things by getting approval just on the pain data. It appears that it's going to stick with its strategy and hope that the numbers are so dramatic that the agency will reverse course. But is that realistic - both for the chances of getting great data and the chances of persuading the FDA? The market doesn't think so. Neither do I.