- Pfizer Inc. and partner Astellas Pharma Inc. said Thursday a late-stage study of their prostate cancer treatment Xtandi helped delay the spread of new tumors in patients with earlier-stage disease, results which could substantially broaden the market for the drug.
- The companies, which split profits from Xtandi in the U.S., plan to seek an expanded approval from the Food and Drug Administration to cover all castration-resistant prostate cancer patients. Xtandi is currently OK'd for use in the metastatic setting.
- Xtandi's broader commercial prospects were a key factor in Pfizer's decision to acquire Medivation, Inc., the drug's original developer, in a $14 billion acquisition last fall. Sales so far this year have come in weaker than the pharma predicted, although company executives expect that trend to reverse.
Xtandi's weak sales in the first quarter sparked questions from analysts of whether Pfizer may have overpaid to acquire Medivation. While the company attributed the slowdown to higher utilization of patient assistance programs, declining year-over-year sales in the U.S. did not inspire confidence in what was supposed to be a premiere cancer drug.
Success in the Phase 3 PROSPER study could largely mitigate those concerns as approval of Xtandi in non-metastatic prostate cancer, if granted, could double the addressable market for the drug.
Results showed adding Xtandi to androgen deprivation therapy (ADT) improved metastasis-free survival compared to ADT alone. Detailed data on the extent of the benefit seen in the study won't be released until an unspecific future medical meeting.
If substantive, however, the drug could fill a key market niche for patients with non-metastatic castrastion-resistant prostate cancer (CRPC).
"Many prostate cancer patients who initiate androgen deprivation therapy will experience disease progression illustrated by a rising PSA level, and currently, there are no FDA-approved treatment options for patients with non-metastatic CRPC until they develop confirmed radiographic metastatic disease," said Neal Shore, a director at the Carolina Urologic Research Center.
Earlier in the year, Pfizer executives identified widening Xtandi's label to earlier disease settings as a key "pivot point" for the franchise. Another study, dubbed EMBARK, is testing Xtandi in non-metastatic hormone-sensitive prostate cancer.
Pfizer and Astellas obtained results from the study two years sooner than would have been expected under the original trial design. The two companies were able to move a read out forward through a protocol amendment which revised the analysis plan for the trial's endpoint and reduced target enrollment for the study by 120 patients.
"After we've seen such a significant hazard ratio in the [other] clinical studies, if this had been developed, designed at this time, it would have been designed with fewer patients," explained Elizabeth Barret, head of Pfizer Oncology, on a Jun. 9 call with analysts.
Shares in Pfizer rose by more than 1.5% in early trading Thursday on the news.