Cabazitaxel Remains Active in Patients Progressing after Docetaxel Followed by Novel Androgen Receptor Pathway Targeted Therapies

Background Cabazitaxel, abiraterone acetate (AA), and enzalutamide have been approved for the treatment of patients with metastatic castration-resistant prostate cancer (mCRPC) following docetaxel chemotherapy. Whether taxanes and next-generation androgen receptor (AR) axis inhibitors are cross-resistant or not is a subject of debate. Objective To evaluate the antitumour activity of cabazitaxel in mCRPC pretreated with abiraterone or enzalutamide. Design, setting, and participants The antitumour activity of cabazitaxel was assessed in patients with mCRPC and progressive disease after treatment with docetaxel and AA. In parallel, cabazitaxel antitumour activity was studied in enzalutamide-resistant models. Outcome measurements and statistical analysis Changes in prostate-specific antigen (PSA) levels and progression-free survival were used to determine the activity of cabazitaxel treatment. Cell proliferation, immunofluorescence, and AR transactivation assay were used in enzalutamide-resistant models. Results and limitations A total of 79 patients who had progressive mCRPC after docetaxel (median: 8 cycles; range: 4-12 mo), and AA (median: 4.8 mo; range:1-55 mo) received cabazitaxel 25 mg/m² every 3 weeks (median: 6 cycles; range:1-15 cycles). A PSA decline ≥30% was achieved in 48 patients (62%; 95% confidence interval [CI], 51-73), and a decline ≥50% was achieved in 28 patients (35%; 95% CI, 25-47). The median progression-free survival and overall survival were 4.4 and 10.9 mo, respectively. In vitro, cabazitaxel decreased cell viability in both enzalutamide-sensitive and enzalutamide-resistant prostate cancer cells within the same range of concentrations. PC3, an AR-negative cell line, exhibited similar sensitivity to cabazitaxel. Conclusions Cabazitaxel and AR-pathway inhibitors are not cross-resistant. Preclinical data suggest that cabazitaxel activity does not act mainly through AR axis inhibition. Patient summary The antitumour activity of cabazitaxel, a chemotherapy agent, was studied in prostate cancer resistant to conventional hormonal therapy and to more recent endocrine therapies (abiraterone or enzalutamide). Cabazitaxel retained anticancer activity in more than half of the cases.