Top-line data from both studies is expected in late 2013 or first half 2014, says Exelixis.
Here are the bullet points summarizing the Exelixis bear thesis of Bio-investor X:
- Exelixis will miss trial enrollment timelines, especially since on top of Zytiga, Amgen's (AMGN) Xgeva and Dendreon's (DNDN) Provenge (all approved and competing for prostate cancer patients), Algeta's Alpharadin and MDV3100 will be approved soon and also have compassionate-use programs in place.
- The trials are mis-modeled; the assumptions for survival in the control arm of study 307 are too low. This will make timing of events (deaths) slower and hamper cabo's ability to beat the control arm (survival benefit) by 30%.
- Study 307 is being conducted at an unproven lower dose of cabo than previously tested, which is likely to reduce the drug's efficacy and make it difficult to win on survival benefit (especially if the control-arm patients live longer than expected.)
- The pain trial, study 306, is of no value on its own for a cancer drug. FDA recognizes three endpoints for prostate cancer drugs -- survival, quality of life and pain reduction -- but if you don't get a survival claim, forget about premium pricing.
Bio-investor's main beef with Exelixis is Study 307, which he predicts is more likely to fail to demonstrate a survival benefit favoring cabo. Without a survival benefit, FDA will not approve cabo, he says.
I turn the Mailbag over to Bio-Investor X:"Exelixis and the analysts supporting the company say study 307 will take a year to enroll, with top-line data ready about a year after full enrollment. This timeline is unrealistic. "Algeta's phase III study of Alpharadin
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