Treatment with Xtandi (enzalutamide) significantly extends the lives of men with high-risk, non-metastatic castration-resistant prostate cancer (CRPC), according to final data from a Phase 3 clinical trial.
Developed by Pfizer and Astellas Pharma, Xtandi is an oral hormone therapy that works by blocking the interaction between male hormones and their receptors in cancer cells. Since this interaction can stimulate prostate cancer growth, Xtandi is expected to halt cancer progression in these patients.
The therapy is currently approved in the U.S. and in Europe for the treatment of three types of advanced prostate cancer: high-risk non-metastatic CRPC, metastatic CRPC, and metastatic castration-sensitive prostate cancer (mCSPC).
Xtandi’s approval for treating men with high-risk non-metastatic CRPC was based on positive data from the Phase 3 PROSPER clinical trial (NCT02003924).
PROSPER was designed to assess whether adding Xtandi to standard androgen deprivation therapy (ADT) was superior to ADT alone in 1,401 men with non-metastatic CRPC and rising prostate-specific antigen (PSA) levels. PSA levels are a marker of disease progression. The patients had no symptoms or other evidence of metastasis.
The participants were randomly assigned to receive either 160 mg of Xtandi (933 patients) or a placebo (468 patients) orally, in addition to standard therapy. The trial’s primary goal was metastasis-free survival, or the time a patient lives without cancer spreading or until death from any cause.
Secondary goals included time to PSA progression and to first use of a subsequent anti-cancer chemotherapy, patients’ overall survival, and safety.
Interim results at an earlier data cut-off date in June 2017 showed that adding Xtandi to ADT significantly reduced the risk of developing metastases or death by 71%, compared with ADT alone.
The combination therapy extended metastasis-free survival and the time to first use of chemotherapy by nearly two years (21.9 months), and the time to PSA progression by almost three years (33.3 months), compared with standard therapy alone.
Median overall survival had not been reached, meaning that half of the patients in each group were still alive. While the risk of death was 20% lower with Xtandi than with placebo, the difference was not statistically significant.
At that time, no significant differences in overall survival were found between the two groups. The results showed that 11% of men in the Xtandi group died compared with 13% in the placebo group.
The researchers noted, however, that most of these deaths occurred in elderly men with a high burden of other coexisting conditions. In addition, more patients receiving the combination therapy died without detectable metastasis development than those in the placebo group.
Xtandi’s safety profile was consistent with previous studies, with fatigue as the most commonly reported adverse event.
The combination treatment was associated with a higher frequency of severe adverse events (31%) than ADT alone (23%). Cardiovascular events — 5% in the Xtandi group vs. 3% among those on placebo — were the main cause of death associated with adverse events.
Now, Pfizer and Astellas Pharma announced new data from the PROSPER final analysis, which showed that adding Xtandi to ADT significantly improved patients’ overall survival compared with ADT alone. Xtandi’s safety profile also was generally consistent with that reported in the previous analysis.
The companies plan to share detailed effectiveness and safety data from PROSPER’s final analysis soon, they said.
Meanwhile, China’s regulatory agency is currently reviewing PROSPER interim data for the approval of Xtandi for the treatment of men with high-risk non-metastatic CRPC.