Pfizer and Astellas have revealed the data behind its regulatory submissions in the US and EU to try to extend the use of Xtandi to include men with early-stage prostate cancer that hasn’t spread to other areas of the body.
The filings are based on the just-released results of the PROSPER trial, which show that adding Xtandi (enzalutamide) to treatment with anti-androgen hormone therapy reduced the risk of disease spreading or death by 71% compared with hormone therapy alone in castration-resistant prostate cancer (CRPC).
Metastasis-free survival (MFS) – the primary endpoint in the much-anticipated study – was improved from 14.7 months on hormone therapy alone to 36.6 months when the androgen receptor inhibitor was added to the regimen. Men in the 1,400-patient trial were recruited on the basis they were at high risk of their cancer spreading.
At the moment Xtandi, in common with a rival therapy from Johnson & Johnson called Zytiga (abiraterone acetate), is only prescribed for men with advanced CRPC that has spread and no longer responds to hormone therapy and, if approved, the new indication would move Xtandi up the treatment chain and could allow it to be used in more patients.
“In patients with non-metastatic CRPC, there is a high unmet need to delay development of metastases and the progression to advanced prostate cancer,” commented Maha Hussain of Northwestern University, the principal investigator for PROSPER. “There are currently no approved systemic therapies for patients with non-metastatic CRPC in the US,” she added.
Pfizer and Astellas will be presenting the data to oncologists at the American Society of Clinical Oncology’s Genitourinary Cancers Symposium later this week.
The two companies hope that the new data will help impart fresh momentum to Xtandi, which was the main asset in Pfizer’s $14bn takeover of Medivation in 2016 but which has not been growing as quickly as its new owner hoped.
Last week, Pfizer reported Xtandi alliance revenues (direct sales plus royalties from Astellas) of $590m in 2017 as a whole, with fourth quarter demand up 26% over the same period of 2016 and 12% higher than the third quarter, suggesting more stable sales growth. The market category will see some significant disruption later this year however when generics of Zytiga reach the big US market.
Pfizer’s chief operating officer Albert Bourla told analysts last week that he does not see generic abiraterone having a big impact on its franchise, as Xtandi has some key advantages, including dosing frequency, no need for co-administration with steroids and no need to monitor patients on a monthly basis.