Pfizer, Astellas' Xtandi lowers risk of metastasis, death in Phase III trial of patients with non-metastatic prostate cancer 

Pfizer and Astellas on Monday unveiled late-stage data illustrating that Xtandi (enzalutamide), in combination with androgen deprivation therapy (ADT), cut the risk of metastasis or death by a significant 71 percent in patients with non-metastatic castration-resistant prostate cancer (nmCRPC), versus ADT alone. Lead investigator Maha Hussain remarked "the findings from the trial are quite impressive in terms of delaying the visibility of the cancer," adding that "the data [are] very likely practice changing." 

The placebo-controlled PROSPER study involved about 1400 patients with nmCRPC who were randomised to treatment with Xtandi plus ADT or ADT alone. In addition to the primary endpoint of metastasis-free survival (MFS), secondary endpoints included overall survival (OS), the time to prostate-specific antigen (PSA) progression and the time to first use of new antineoplastic therapy. 

Results showed that median MFS was 36.6 months for the Xtandi arm, compared with 14.7 months for ADT alone. Further, patients given Xtandi plus ADT had a 93-percent reduction in relative risk of PSA progression compared to those on ADT alone, while the median time to first use of new antineoplastic therapy was 39.6 months and 17.7 months, respectively. The drugmakers noted that while the median OS had not yet been reached at the time of the first interim analysis, these "interim results demonstrated a trend in favour of Xtandi that was not statistically significant."

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Pfizer and Astellas noted that the adverse event profile of Xtandi in the PROSPER study was in line with previous trials of patients with mCRPC. The companies said marketing applications based on the PROSPER results, which will be presented at the upcoming ASCO Genitourinary Cancers Symposium, have been submitted to the FDA and the European Medicines Agency.

"The treatment opportunities are almost double than the current indication," commented Albert Bourla, chief operating officer at Pfizer, "and the financial interest is larger because the duration of treatment is longer."

Xtandi is approved in the US and EU for use in chemotherapy-naïve men with metastatic castration-resistant prostate cancer. The drug has also been cleared in the US and Europe for previously treated patients with metastatic castration-resistant prostate cancer. Astellas and Medivation had been partnered on Xtandi since 2009, with Pfizer gaining rights to the therapy as part of its $14-billion purchase of Medivation in 2016. 

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