Cross resistance suspected between abiraterone and taxane chemotherapy

This study evaluated the effectiveness of taxane-based chemotherapy after treatment with abiraterone (Zytiga), to determine whether resistance to androgen blockade also affects the outcome of taxane treatment.

Castration-resistant prostate cancer refers to cancer that has progressed despite androgen deprivation therapy (treatment intended to reduce the production or effect of androgen hormones such as testosterone). Chemotherapy is often indicated in the treatment of castration-resistant prostate cancer, and taxane-based agents, such as docetaxel, are often the first choice.

Abiraterone (Zytiga), a relatively new anti-androgen drug, was initially only approved for the treatment of castration-resistant prostate cancer after chemotherapy. However, due to successful treatment results many physicians currently prescribe abiraterone early during the course of treatment. Recent studies have suggested that since taxane-based chemotherapy and abiraterone are effective partially due to similar mechanisms, prior abiraterone treatment may contribute to taxane resistance and decreased chemotherapy effectiveness.

The study included 119 patients with metastatic (wide spread) castration-resistant prostate cancer, all treated with docetaxel. 24 of the patients were previously treated with abiraterone before initiation of chemotherapy.

Good response to docetaxel chemotherapy (assessed by reduction in PSA levels) was significantly less common among patients previously treated with abiraterone. 38% of patients receiving abiraterone before docetaxel chemotherapy showed significant PSA reductions in response to treatment, compared to 63% of patients not previously treated with abiraterone.

Among patients receiving abiraterone before docetaxel chemotherapy, the average time before disease progression (referred to as progression free survival) was 4.4 months. In comparison, average progression free survival was 7.6 months among patients not receiving abiraterone before docetaxel chemotherapy.

This study concluded that prior abiraterone treatment significantly reduces the effectiveness of taxane-based chemotherapy. These finding suggest that abiraterone treatment should be reserved for patients who have progressed despite chemotherapy, or that a different chemotherapy agent should be enlisted in the treatment of patients already treated with abiraterone.

This study included only a small number of patients, and even a smaller number of patients previously treated with abiraterone. Larger studies are necessary to confirm these results.