GU Symposium 2016: Even After Antiandrogen Therapy, Docetaxel Remains Useful in Prostate Cancer
A study presented at the 2016 Genitourinary Cancers Symposium showed that 40% of patients with metastatic castration-resistant prostate cancer treated with docetaxel following abiraterone (Zytiga) had at least a 50% reduction in prostate-specific antigen (PSA), demonstrating the activity of this drug sequencing. These findings were presented at the Symposium by Flaig et al (Abstract 168).
“The chemotherapy docetaxel used to be our first-line therapy for [metastatic castration-resistant prostate cancer]. Now we use androgen receptor–targeted therapy first. The question was whether docetaxel still has a role in these patients treated with abiraterone. We're no longer using docetaxel first—should we even be using it second?” asked Thomas W. Flaig, MD, Associate Director for Clinical Research at the University of Colorado Cancer Center and Associate Professor of Medicine at the University of Colorado School of Medicine.
Study Findings
The multi-institution study followed 1,088 patients treated on the clinical trial COU-AA-302, which provided the data that led to the approval of abiraterone as a first-line therapy.
“Basically, we wanted to know how these patients were treated after the trial,” said Dr. Flaig.
Sixty-seven percent of the patients treated with abiraterone went on to receive further therapies, with 36% receiving two additional therapies and 17% receiving three or more. About half of all abiraterone-treated patients on the study were treated with docetaxel in the next line of therapy. Of these patients treated with docetaxel immediately after abiraterone, 40% had PSA decline by more than half, demonstrating the effectiveness of this chemotherapy even after treatment with androgen-deprivation therapy.
“Surprisingly, the next most common ‘treatment’ in this setting after docetaxel was no treatment at all,” Dr. Flaig said. Compared with younger patients, those older than 75 years were about twice as likely to receive no subsequent therapy.
Dr. Flaig noted that the trial itself ended in 2010, before the approval of the drug enzalutamide (Xtandi), which is also used as a prechemotherapy treatment for metastatic castration-resistant prostate cancer, likely meaning that more patients of all ages are now receiving additional antiandrogen therapy prior to the use of chemotherapies, including docetaxel.
“This confirms the activity of abiraterone followed by docetaxel and represents important data on the sequencing of medical therapies under this new paradigm,” Dr. Flaig said. “The fact that a substantial portion of patients received no subsequent therapy after the study was done needs additional study to be certain we are maximizing effective therapy for these patients.”
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