Findings from the phase III placebo-controlled SPARTAN trial suggest that apalutamide is an effective treatment for men with non-metastatic castration-resistant prostate cancer (nmCRPC) who are at high risk for developing metastatic disease, and for whom no approved treatments exist.

Men who received apalutamide had a 72% lower risk of metastasis or death than those who received placebo.

These findings, which according to the authors may be relevant to about 100,000 men in the United States, will be presented at the upcoming 2018 Genitourinary Cancers Symposium in San Francisco, California.

“Until this trial, there have been no drugs proven to benefit men with non-metastatic prostate cancer that has progressed despite standard hormonal therapy. These results show that apalutamide made a significant difference in prolonging the time before the development of metastasis,” said lead study author Eric J. Small, MD, FASCO, professor of medicine at the University of California, San Francisco.

The findings from the SPARTAN trial are discussed here by Prof Kurt Miller, Prof Silke Gillessen, Prof Heather Payne and Dr Eric Small. 

Castration-Resistant Prostate Cancer

Many men with prostate cancer recurrence following local treatment with surgery or radiation therapy are treated with hormonal therapy, termed androgen deprivation therapy (ADT).

Prostate cancer that subsequently develops resistance to ADT is termed castration-resistant.

There are no FDA approved agents for the treatment of non-metastatic castration resistant prostate cancer (nmCRPC), and some physicians advocate watchful waiting for these patients.

However, men whose prostate-specific antigen (PSA) score is rapidly rising while on ADT (with a PSA doubling time of less than 8 to 10 months) are at a significantly increased risk of developing metastases or death.

This group represented the men enrolled in the SPARTAN study.

About the Study

The SPARTAN Study was conducted at 332 institutions worldwide and enrolled 1,207 men.

People with nmCRPC that had stopped responding to ADT and who were at high risk of metastasis based on a PSA doubling time of 10 months or less were randomly assigned to receive apalutamide or placebo taken as daily tablets, added to ongoing ADT.

At the time of development of metastases, patients were treated with standard second therapies at their physician’s discretion and had an option to receive on-study abiraterone acetate and prednisone, a standard of care.

Key Findings

The median PSA doubling time at study entry was approximately 4.5 months in both the apalutamide and placebo groups.

Apalutamide decreased the risk of metastasis and death by 72% compared with placebo and significantly prolonged the median metastasis-free survival by 2 years (40.5 months in the apalutamide group vs 16.2 months in the placebo group).

At this interim analysis for overall survival, researchers also noted a trend favouring improved overall survival for men receiving apalutamide versus placebo, although the difference was not statistically significant.

Following the analysis of metastasis-free survival, study treatment was unblinded in July 2017 following the recommendations of an Independent Data Monitoring Committee, and all patients were offered open-label apalutamide.

Apalutamide was well tolerated, with 10.7% of men discontinuing treatment due to adverse events, compared with 6.3% of men receiving placebo.

Quality of life scores were maintained in those men receiving apalutamide added to ADT.

“These data demonstrate that the use of apalutamide prior to the development of metastases clearly benefited patients whose prostate cancer no longer responded to conventional hormonal therapy,” said Dr. Small.

“It is exciting that there now exists such a well-tolerated agent for this group of high-risk patients for whom no approved therapies currently exist.”

Next Steps

The authors hope to identify those patients who benefited the most from apalutamide by analysing molecular and circulating markers from blood samples. 

They will also look in greater depth at patient-reported outcomes that evaluate the trial success or failure from a patient perspective.

Source: 2018 Genitourinary Cancers Symposium