STAMPEDE: Abiraterone Slowed Progression of Advanced Prostate Cancer

June 3, 2017

Abiraterone at the start of ADT for men with metastatic prostate cancer significantly improved overall survival and failure-free survival, with manageable toxicity.

CHICAGO-Adding abiraterone at the start of androgen deprivation therapy (ADT) for men with high-risk locally advanced or metastatic prostate cancer significantly improved overall survival and failure-free survival, with a manageable toxicity profile, according to the results of the STAMPEDE trial (abstract LBA5003) presented at the 2017 American Society of Clinical Oncology (ASCO) Annual Meeting, held June 2–6.

“Abiraterone acetate plus prednisone improves survival for men with hormone-naive prostate cancer starting long-term hormone therapy for the first time,” said researcher Nicholas James, BSc, MBBS, PhD, professor of clinical oncology at Queen Elizabeth Hospital in Birmingham, United Kingdom.

Abiraterone stops production of testosterone and other androgens throughout the body. ADT slows prostate cancer growth by preventing the testicles from making testosterone; however, other organs in the body still produce small amounts of testosterone and other androgens.

The STAMPEDE trial was a multi-arm, multi-stage trial that recruited patients with high-risk locally advanced or metastatic prostate cancer starting long-term ADT. The trial randomly assigned 1,917 patients to standard of care (ADT for at least 2 years) with or without abiraterone 1,000 mg plus prednisone 5 mg daily. Men with locally advanced cancer could also receive radiation therapy. The primary outcome measure was death from any cause.

The median age of patients was 67 years, and 52% had distant spread of disease.

With a median follow-up of 40 months, 262 deaths occurred with standard of care and 184 occurred with the abiraterone regimen. The addition of abiraterone lowered the relative risk for death by 37% compared with standard of care (hazard ratio [HR], 0.63; 95% CI, 0.52–0.76; P = .0000012). The 3-year survival rate was 76% for standard of care compared with 83% for patients assigned to abiraterone.

“Because we have a broader range of patients, we are nowhere near the median survival for the control arm, yet alone the experimental arm,” James said. “Our projections are that for the experimental arm for the metastatic part of the comparison, the median survival will go from about 3.5 years to around 6.5 years with abiraterone. This is one of the biggest survival gains ever reported in a trial of an adult solid tumor.”

In addition, James said that this survival benefit seems to be for the whole trial population, regardless of metastatic status. When looking at the data based on metastatic status, the survival-even though there are very few deaths so far in non-metastatic patients-appears to be similar.

Finally, abiraterone lowered the relative chance of treatment failure by 71% compared with standard of care (HR, 0.29; 95% CI, 0.25–0.34; P = 0.377 x 10-61).

Commenting on the study, ASCO Expert Sumanta Kumar Pal, MD, pointed out that several years ago the STAMPEDE trial showed the benefits associated with chemotherapy added to conventional hormone therapy for metastatic prostate cancer. Here, the same study backbone is used to show the benefit of abiraterone.

Pal pointed out that one of the unique aspects of the STAMPEDE trial was the inclusion of patients with non-metastatic disease.

“Although Dr. James shows the degree of benefit in survival is similar in non-metastatic and metastatic patients, I would argue that further study is needed to determine appropriate candidates for abiraterone who have non-metastatic disease,” James said. “These issues notwithstanding, abiraterone should change the treatment paradigm for patients with newly diagnosed metastatic prostate cancer and largely displaces chemotherapy from the current paradigm.”