Development of a predictive model of PSA response to a switch from prednisone to dexamethasone in metastatic castrate-resistant prostate cancer patients biochemically progressing on abiraterone.

Abstract

88 Background: Abiraterone acetate (AA) is typically administered with prednisone (P) to prevent symptoms of mineralocorticoid excess in patients with metastatic castrate resistant prostate cancer (mCRPC). After biochemical progression on AA + P, there is a sizeable subset of patients who have a renewed PSA response when switched from P to dexamethasone (D). The purpose of this study was to delineate clinical and pathologic factors that are predictive of a PSA response to such a steroid switch. Methods: We performed a retrospective analysis of 87 patients switched from AA+P to AA+D at Sunnybrook Odette Cancer Centre (Toronto, ON, Canada) between December 2012 and September 2018. Information on demographics, disease characteristics, previous treatments and performance status was collected. Response to the P to D switch maneuver was defined as a decrease in PSA by ≥30% within 12 weeks of the intervention (PSA30). Univariate logistic regression analyses were used to create a prediction model for each covariate tested, and R2 was applied for the measure of fit.Using multivariable logistic regression analysis and a backward stepwise selection procedure, we sought to identify patient and/or disease characteristics associated with a PSA30. Results: 38/87 patients (44%) experienced a PSA30. Univariate analysis showed that a favourable ECOG performance status, no prior docetaxel and no prior enzalutamide use were associated with a PSA30. On multivariable logistic regression analysis both favourable ECOG performance status and no prior enzalutamide use remained associated with a PSA30 (Table). Conclusions: A considerable proportionof patients with mCRPC who biochemically progress on AA+P have a renewed PSA response when changed to AA+D.Patients with a favourable ECOG performance status and no prior enzalutamide use are more likely to respond to such a steroid switch. Further prospective studies are needed to validate our findings.[Table: see text]