Antiandrogen withdrawal (AAWD) in patients (pts) with prostate cancer (PCa): Retrospective analysis of data from the South Australian Prostate Cancer Clinical Outcome Collaborative (SA-PCCOC).

Abstract

240 Background: In 15-30% of pts with metastatic PCa who progress on Maximal Androgen Blockade (MAB), withdrawal of the antiandrogen agent (AAWD) and continuing the LHRH agonist alone, leads to PSA decreases of ≥50% and prolonged progression free survival. Here we describe patient and disease characteristics, treatment history and outcomes of pts who have been managed with AAWD. Methods: Data were obtained from SA-PCCOC (a longitudinal, observational registry of biopsy-proven PCa cases, throughout the Australian state of South Australia since 1998). Proportions were compared using a Chi squared test. A multivariable model used competing risks (Fine and Gray) and Cox proportional Hazards models to assess overall survival and Prostate cancer specific mortality (PCSM). Survival was calculated from the date of rising PSA for patients on LHRH and AA. Results: 140 pts were found to have MAB. Of these, 31(22.1%) had AAWD. In the AAWD group, median age was 81y (51-95). Age at diagnosis, Gleason score at biopsy and diagnostic PSA were not significantly different amongst the two groups. Treatment PSA was significantly lower in the AAWD group (20.55 (range 0.6-9,995) vs 50.50 (range 0.95-4378) p= 0.02). There was a significant association of AAWD with PCSM (sHR 0.35, 95% CI 0.16-0.76; p = 0.008). Also significant in the model was prior time on hormones (sHR [per month increase] 0.96 95% CI 0.95-0.98, p<0.001). There was also a significant association of AAWD with overall survival (HR 0.22, 95% CI 0.10-0.46; p <0.001). Again, prior time on hormones was also significant (HR [per month increase] 0.96 95% CI 0.95-0.98, p<0.001). Multivariate analysis was performed on data from 80 pts (60 pts omitted due to missing data). Conclusions: Pts in whom AAWD was used were older and had lower treatment PSA. In this small cohort, AAWD was associated with both reduced PCSM and overall risk of death. The time spent on MAB also appeared to be significant. This retrospective observational study may be subject to confounding, however the observation warrants further investigation in larger cohorts and in a prospective setting.