Pfizer (NYSE:PFE)
- 20.2 month PFS for palbociclib + letrozole vs. 10.2 month for letrozole + placebo
- Overall survival 37.5 months for palbociclib vs 33.3 months for placebo (not statistically significant)
- OS data still maturing based on only 65 events
- Company believes approval can be gained based on PFS
Palbociclib Results - Highly Anticipated by Market
Ever since positive top-line results for the PALOMA-1 study were announced on February 3rd, investors have been eagerly awaiting full data disclosure including key information regarding the secondary endpoint of overall survival (how long patients survive on therapy vs on placebo). On Sunday at the American association of Cancer Research (AACR) annual meeting, Pfizer revealed the detailed data from the study.
The PALOMA-1 study was a phase 2 study investigating the combination of Pfizer's palbociclib plus letrozole vs. letrozole plus placebo in post-menopausal women with Estrogen Receptor positive (ER+) and Human epidermal growth factor receptor 2 negative (HER2-) locally advanced or metastatic breast cancer. The ER+ HER2- population represents about 60% of advanced breast cancer cases.
Based on the strong interim results reported in February, investors have been awaiting the overall survival data from this phase 2 trial to help determine whether or not Pfizer would be able to file for accelerated approval base don the phase 2 data alone.
Market expectations seem to have gotten ahead of the actual data. In a population where the median overall survival is nearly 3 years, showing a statistically significant OS benefit from just 39% of the events from a 165 patient trial is, in our view, unrealistic. For example, after disease progression, differences in follow-on therapies can confound overall survival in such a small study.
Strong PFS Benefit May Be Approvable
The 20.2 month progression free survival vs 10.2 months for letrozole alone is a highly encouraging result. Given that the overall survival was numerically better (though not statistically significant) our view is that the data are indicative of an active drug that is potentially approvable. Ongoing phase 3 studies (PALOMA-2 and PALOMA-3) whose final data collection dates are in 2015 will determine the ultimate fate of Palbociclib.
During their conference call to discuss the PALOMA-1 data, Pfizer indicated that they believe that in the ER+ HER2- population, approval with a PFS benefit with a trend towards an overall survival advantage is a possibility. However, the company would not offer specific guidance regarding the timing of an NDA filing.
Takeaway
Because of the strong PFS results announced in February, we believe that market expectations were ahead of the actual data in the PALOMA-1 study. The lack of a statistically significant overall survival benefit, while not unexpected for a trial of this size, will nevertheless be viewed negatively by the markets because an overall survival benefit was likely priced in to the stock. Indeed, 54% of buy-siders surveyed by ISI Group's Mark Schoenebaum, felt that the data released today were "a bit worse" than their expectations of the data ahead of the event. Another 11% said that the data were "much much worse" than their expectations. 30% said the data was in-line with their expectations and just 5% indicated that the data was better than their expectations.
