Exelixis also fully intends to later expand cabo's use in prostate cancer with two additional phase III trials, one of which will definitely use overall survival as the primary endpoint.
Doubter and skeptics argue that mitoxantrone is an old, rarely used prostate cancer drug reflecting outdated thinking. FDA more recently has required new prostate cancer drugs to demonstrate a survival benefit and cabo should be no exception. Proving a survival advantage will be an extreme challenge for Exelixis, the bears say, because the patients the company plans to enroll in the initial phase III study have advanced disease and cabo is not an easy drug to tolerate from a side-effect perspective.
Dr. Daniel George, a prostate cancer expert at Duke University and an investigator in previous cabo studies, said focusing the initial pivotal study on pain relief takes advantage of the drug's strength and is clinically meaningful to these advanced prostate cancer patients.
"I think the FDA will find it hard to ignore since none of the other [prostate cancer] drugs have a very good track record with respect to pain," he said.If Exelixis is right and FDA clears an SPA with a bone/pain endpoint (without requiring a survival benefit), Exelixis' stock should move higher. The more interesting, uncertain and evolving story, in my mind, is how the efficacy and safety of Exelixis' cabo stacks up against Algeta's Alpharadin in a similar prostate cancer patient population. Algeta will be seeking U.S. approval soon with a study that demonstrated a survival benefit.
Leighton H. writes, "Wow! You have been silent in regard to Cell Therapeutics (CTIC) lately. No comment about the confirmation of the significance of the PIX301 trial by the independent radiological review, or the upcoming EMA decision on pixantrone, or the reconsideration of the FDA decision in regard to pixantrone. Last I heard from you were comments to your blog some months ago where, when asked about your thoughts on the chances of approval of pixantrone by the FDA, you stated '0% chance.' Do you still hold the same opinion?" I do, although I believe the question to me dealt with Cell Therapeutics' chance of winning pixantrone approval based on the appeal of the FDA's 2010 rejection. This is what I wrote about the pixantrone appeal last December: "The FDA appeal is a desperate Hail Mary that is highly unlikely to succeed. I also fail to see a scenario by which European regulators reach a more positive conclusion about pixantrone compared to their U.S. counterparts at FDA." I don't see any reason to amend that prediction, a year later.
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