- Pfizer Inc. and partner Astellas Pharma Inc. announced full data on Monday afternoon for their prostate cancer drug Xtandi from the Phase 3 PROSPER study.
- Topline results were announced in September and the companies have filed applications with both the U.S. Food and Drug Administration and the European Medicines Agency to gain broader approval for the drug.
- While sales of Xtandi have been weaker than expected, approval in the non-metastatic castration-resistant prostate cancer (CRPC) setting could greatly increase its prospects.
Driving Pfizer’s $14 billion acquisition of Medivation, Xtandi (enzalutamide) has long failed to live up to expectations. The drug brought in about $2 billion in worldwide sales during the first nine months of fiscal year 2017, but an approval based on the PROSPER clinical trial results could double the potential patient population. Pfizer has said that the drug would reach over $1 billion in U.S. annual sales by 2020, but investors have been skeptical.
Approved in 2012 for the metastatic setting, the results could move Xtandi forward in the treatment paradigm, making it available to patients who are not as sick.
The Phase 3 PROSPER study, presented at the 2018 Genitourinary Cancers Symposium in San Francisco, showed Xtandi and androgen deprivation therapy (ADT) reduced the risk of metastases and death by 71% compared with ADT alone in patients with non-metastatic CRPC.
The 1,400-patient trial found that men who received Xtandi on top of ADT had metastasis-free survival of 36.6 months compared with 14.7 months on ADT alone.
The Xtandi combo delayed the time to prostate-specific antigen (PSA) progression by 33.3 months, reducing risk by 93%.
Xtandi plus ADT prolonged the time to first-use of antineoplastic therapy by 21.9 months.
At the time of the interim analysis, overall survival had not yet been reached in either treatment arm, but the companies said it was trending in Xtandi’s favor.
Evercore ISI analyst Umer Raffat worried in a September note that overall survival is the "gold standard" in this setting and that regulators might not approve the drug for this indication based on the metastasis-free survival endpoint alone.