Final data from a late-stage trial of Astellas' and Medivation's prostate cancer drug Xtandi (enzalutamide) show that use of the drug in patients with few disease symptoms can offer a survival benefit and also delay the start of treatment with chemotherapy.

In the Phase III PREVAIL trial, which included pre-chemo patients with metastatic prostate cancer whose disease progressed despite androgen deprivation therapy, Xtandi demonstrated a statistically significant overall survival benefit compared with placebo, reducing the risk of death by 29%, according to the firms.

The drug was also shown to significantly cut the risk of radiographic progression or death by 81% compared with placebo treatment and, also importantly, patients taking Xtandi experienced a 17-month delay in the time to the start of chemotherapy. 

In another show of its potential benefit, almost four out of five patients taking the drug experienced a decline in PSA of 50% or more compared to less than 4% in the placebo group. 

On the safety side, the most common side effects presenting more frequently in the treatment group included fatigue, back pain, constipation and arthralgia. 

Hypertension seemed to occur more frequently in the treatment group versus placebo, at 13.4% versus 4.1%, respectively, while grade 3 or higher cardiac adverse events were reported in 2.8% of the Xtandi group versus 2.1% of placebo-treated patients. 

According to principal study investigator Tomasz Beer, also a professor of medicine and deputy director of the Knight Cancer Institute at Oregon Health & Science University, data from the trial "demonstrate for the first time a statistically significant reduction both in the risk of death and a delay in cancer progression in men with metastatic prostate cancer who have a rising PSA and few, if any, symptoms".

Step forward for patients

"The scope of the efficacy endpoints and the safety profile in PREVAIL, including the length of time that chemotherapy can be delayed, would represent a step forward for men with prostate cancer," he stressed.

On the back of the results, Astellas and Medivation said they plan to submit regulatory applications to US and European agencies early this year to expand Xtandi's remit to pre-chemo patients (it is already approved to treat metastatic prostate cancer in patients who have already had chemotherapy).

If successful, this could significantly expand the patient population and thus increase sales.