Abiraterone Acetate May Benefit Some Prostate Cancer Patients With High Gleason Scores

December 9, 2015
John Schieszer

The study demonstrated that treatment of abiraterone acetate was associated with longer overall disease control, even when a very high Gleason score indicated especially aggressive cancer.

Based on radiographic progression-free survival (rPFS) and overall survival (OS), patients with prechemotherapy or postchemotherapy metastatic castration-resistant prostate cancer (mCRPC) should be considered candidates for abiraterone acetate (Zytiga), regardless of Gleason score at initial diagnosis, according to researchers at the University of Colorado. 

Researchers have published a study in the Annals of Oncology indicating that a high mCRPC Gleason score should not be considered in the decision to treat with abiraterone acetate. The researchers contend that tumor metastases may no longer reflect the histology at the time of diagnosis.

The investigators conducted a study that included patients who were followed in two different trials: COU-AA-301 (NCT00638690) and COU-AA-302 (NCT00887198). The researchers obtained initial diagnosis Gleason scores in 1,048 patients of 1,195 patients in COU-AA-301 (postdocetaxel) and 996 patients of 1,088 in COU-AA-302 (chemotherapy-naïve) patients treated with abiraterone acetate plus prednisone.

The study demonstrated that treatment of abiraterone acetate was associated with longer overall disease control, even when a very high Gleason score indicated especially aggressive cancer. The researchers found that patients with a Gleason score greater than 8, postdocetaxel treatment with abiraterone acetate extended progression-free survival  (PFS) from 5.5 months to 6.4 months, and prechemotherapy abiraterone treatment extended PFS from 8.2 months to 16.5 months.

Thomas Flaig, MD, who is the medical director of the University of Colorado Cancer Center’s Associate Director for Clinical Research and associate professor of medicine at the University of Colorado School of Medicine, Denver, said in a press release that most clinicians feel that with an unfavorable Gleason score, it is best to “immediately reach for the harshest chemicals.” However, these new findings suggest that’s not always the case. Dr. Flaig said abiraterone acetate is easier to take, has fewer side effects, and shows prolonged survival.

Dr. Flaig, who was co-investigator of clinical trials that led to FDA approval of abiraterone acetate, has been exploring how best to use this agent in men with prostate cancer. He said previous studies have suggested that abiraterone acetate is useful even in cases where prostate cancer has metastasized to the liver. The current study extends this finding to include all aggressive prostate cancers marked by a high Gleason score, according to Dr. Flaig.

In addition to extending the duration of PFS, this study showed greater OS and better control of prostate-specific antigen (PSA) with abiraterone acetate treatment. While more studies are warranted, Dr. Flaig said these findings may help better guide clinicians on how best to use this treatment.  He said clearly there are cases in which cytotoxic chemotherapies are appropriate. However, he said this study points to a broad use of this oral antihormonal agent.