In 1048 prostate cancer patients previously treated with docetaxel and 996 metastatic, castration-resistant patients, treatment with the androgen-lowering drug abiraterone acetate (Zytiga) led to longer overall disease control, even when a very high Gleason score indicated especially aggressive cancer. Results recently published in the Annals of Oncology show that for patients with Gleason score greater than 8, post-docetaxel treatment with abiraterone extended progression-free survival from 5.5 months to 6.4 months, and pre-chemotherapy abiraterone treatment extended progression-free survival from 8.2 months to 16.5 months.
"We have the idea that with an unfavorable Gleason score, we have to immediately reach for the harshest chemicals, but this study shows that's not always the case. Abiraterone is easier to take, has fewer side effects, and shows prolonged survival," says Thomas Flaig, MD, 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.
Flaig was co-investigator of clinical trials that led to FDA approval of abiraterone acetate, and with collaborators continues to explore the best use of the drug. Previous work showed that the drug is useful even in cases of prostate cancer that has metastasized to the liver, another poor prognostic sign. The current study extends this finding to include all aggressive prostate cancers marked by high Gleason score.
"The main thing this analysis does is help us better understand how to use this new agent. Certainly there are cases in which cytotoxic chemotherapies are appropriate. But this study points to a broad use of this oral hormonal agent," Flaig says.
In addition to extending the duration of progression-free survival (the time during which a patient's prostate tumor does not grow), this study showed greater overall survival and better control of prostate-specific antigen (PSA) with abiraterone treatment. The treatment is used in combination with prednisone.
"Thus, the Gleason score at the time of diagnosis should not factor into the decision to prescribe or treat a patient with metastatic castration-resistant prostate cancer with abiraterone acetate plus prednisone," the authors write.