A study presented at the 2016 Genitourinary Cancers Symposium shows that 40 percent of patients with castration-resistant metastatic prostate cancer (mCRPC) treated with docetaxel following abiraterone had at least 50 percent reduction in prostate specific antigen (PSA), demonstrating the activity of this drug sequencing.
"The chemotherapy docetaxel used to be our first-line therapy for mCRPC. 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?" says Thomas W. Flaig, MD, associate director for clinical research at the University of Colorado Cancer Center, associate professor of medicine at the University of Colorado School of Medicine, and one of the study's principal investigators.
The multi-institution study followed 1088 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," Flaig says.
Sixty-seven percent of the patients treated with abiraterone went on to receive further therapies, with 36 percent receiving two additional therapies and 17 percent receiving three or more. About half of all Abiraterone-treated patients on the study were treated with docetaxel in the next subsequent line of therapy. Of these patients treated with docetaxel immediately after abiraterone, 40 percent 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 doecetaxel was no treatment at all," Flaig says.
Compared with younger patients, patients older than 75 years were about twice as likely to receive no subsequent therapy. Flaig notes that the trial itself ended in 2010, before the approval of the drug enzalutamide which is also used as a pre-chemotherapy treatment for mCRPC, likely meaning that more patients of all ages are now receiving additional anti-androgren 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," Flaig says. "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."