Abiraterone acetate plus prednisolone (abiraterone) is approved for patients with mCRPC who have failed docetaxel. Some studies suggest an early PSA-response (≥50% reduction from baseline PSA) by week 4 is associated with improved survival, although data are conflicting.1, 2
This study aimed to investigate the relationship between timing of PSA-response and survival outcomes in mCRPC patients treated with post-docetaxel abiraterone.
We conducted a retrospective audit of mCRPC patients treated at Eastern Health with post-docetaxel abiraterone between September 2011 and September 2016. Data regarding baseline demographics, disease characteristics, treatment, haematological and biochemical parameters and survival outcomes were recorded. PSA-response by weeks 4, 8 and 16 was calculated.
Fifty-five patients treated with post-docetaxel abiraterone were screened to identify 36 patients with available early PSA values. The median age was 70 years. Patients had received a median of 8 cycles of docetaxel. By weeks 4, 8 and 16 a PSA-response had been achieved by 31%, 36% and 39% of patients respectively.
The median duration of abiraterone treatment for patients who achieved a PSA-response by week 4 was 8.0 months, and by week 16, was 7.5 months; for those who did not achieve a PSA-response by week 16, it was 5 months.
The median overall survival (OS) of patients who achieved a PSA-response by week 4 compared to those who did not was 11.9 versus 11.7 months (HR 0.80, 95%CI 0.34-1.87; p=0.34); for those who achieved a PSA-response by week 16 compared to those who did not, median OS was 11.9 versus 11.7 months (HR 0.80, 95%CI 0.36-1.99; p=0.38).
This study suggests an early PSA-response to post-docetaxel abiraterone may not predict significantly improved survival. However, non-routine PSA measurement introduced strong selection bias in this cohort. Prospective assessment of early efficacy signals should be encouraged.