The EU medicines regulator has started its review of Astellas and Pfizer’s prostate cancer drug Xtandi in what looks likely to become a hotly contested indication - non-metastatic castration-resistant prostate cancer (nmCRPC).

The EMA has started its review of Xtandi in this indication based on the results of the phase III PROSPER trial in men with early-stage prostate cancer that hasn’t spread to other areas of the body. Reported in February, the study showed 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.

While the majority of early-stage prostate cancer patients are managed effectively by hormonal therapy, around 10-20% of prostate cancer cases are castration-resistant, and up to 16% of these patients show no evidence that the cancer has spread at the time that status is diagnosed.

At the moment Xtandi - like longstanding rival Zytiga (abiraterone acetate) from Johnson & Johnson - is only prescribed for men with advanced CRPC that has spread and no longer responds to hormone therapy. So, if approved the new indication would move Xtandi up the treatment chain and could allow it to be used in more patients.

Pfizer and Astellas have a fight on their hands trying to tap into this new patient population, however, as J&J has already claimed approval for new therapy Erleada (apalutamide) in nmCRPC in the US, and filed for approval of its drug in Europe last month. The FDA green light came on the back of the SPARTAN study, which showed an extension in metastasis-free survival in nmCRPC versus placebo when given on top of hormonal therapy.

Both SPARTAN and PROSPER have been hailed by oncologists as a major treatment advance in these patients, but for now it’s unclear which of the two drugs will win the marketing tussle. Erleada is the first to claim approval, but Xtandi benefits from longstanding familiarity in CRPC treatment.

Analysts have estimated that nmCRPC could represent a $1bn-plus market in its own right, so expect a fierce battle for supremacy.