Astellas, Pfizer's Prostate Cancer Drug Slays in Phase III Study

Clinical Drug

Late-stage data shows the use of Pfizer’s prostate cancer drug Xtandi (enzalutamide) plus androgen deprivation therapy (ADT) significantly reduced the risk of developing metastases or death by 71 percent.

Pfizer and its development partner Astellas Pharma released data late Monday showing the treatment efficacy in patients with non-metastatic Castration-Resistant Prostate Cancer (CRPC). The companies said the median time for the primary endpoint of metastasis-free survival (MFS), was 36.6 months for men who received Xtandi in comparison to 14.7 months for those who only had the ADT treatment.

Prostate cancer is the second most common cancer in men worldwide, with about 164,000 expected diagnoses in the United States this year. Castration-resistant prostate cancer refers to the subset of men whose prostate cancer progresses despite castration levels of testosterone. Xtandi was approved in 2012 for late-stage prostate cancer.

Not only did the combination of Xtandi and ADT reduce the risk of metastases, trial data showed the combination had a 93 percent reduction in relative risk of prostate-specific antigen (PSA) progression, a biomarker tied to the worsening of a disease, compared to patients who received ADT alone. The combination delayed the median time to PSA progression by 33.3 months compared to 3.9 months of ADT treatment alone.

The combination also prolonged the median time to first use of new antineoplastic therapy by 21.9 months versus ADT alone, Astellas and Pfizer announced.

Although median overall survival rates have not yet been determined, the companies said interim results demonstrated a “trend in favor of Xtandi that was not statistically significant.”

Maha Hussain, of the Robert H. Lurie Comprehensive Cancer Center of Northwestern University and the lead investigator of the trial, said there is a high unmet need for treatments that will delay development of metastases or delay the progression to advanced prostate cancer in patients with non-metastatic CRPC. There are currently no approved systemic therapies for patients with non-metastatic CRPC in the United States, Hussain said, which further underscores the significance of the Phase III results.

“In the Prosper trial, treatment with enzalutamide plus ADT delayed the development of metastases compared to standard of care ADT alone and, if approved, may provide men with non-metastatic CRPC an important new treatment option,” Hussain said.

Full data from the trial will be presented later this week at the 2018 Genitourinary Cancers Symposium in San Francisco.

The data from the Phase III Prosper trial has been sent to the U.S. Food and Drug Administration and European Medicines Agency to support regulatory approval. If approved, the companies hope the combination therapy will give it a leg up over Johnson & Johnson’s Zytiga. Last summer, J&J presented data that showed its combination of Zytiga, ADT and prednisone was a potent combination in treating high-risk metastatic hormone-sensitive prostate cancer (HSPC).

Astellas and Pfizer said adverse events in the Prosper Trial were consistent with previous enzalutamide clinical trials in patients with metastatic CRPC. Grade 3 or higher adverse events, such as hypertension, were reported in 31 percent of men treated with XTANDI plus ADT and in 23 percent of men treated with ADT alone.

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