A phase II trial of abiraterone acetate (AA) without prednisone in castration resistant prostate cancer (CRPC).

Abstract

5040 Background: AA blocks CYP17 and suppresses adrenal androgens and glucocorticoids. Given the risk of mineralocorticoid excess (ME), AA is administered with corticosteroids. In this phase II multicenter, single-arm study, we assess the safety of AA without steroids in CRPC. The primary objective is to determine the proportion of men requiring prednisone to manage ME. Methods: Eligible patients had CRPC with controlled blood pressure (BP) ( < 140/90 on ≤3 agents) and a normal or ≥3.5 mmol/L potassium. Patients initially received AA (1000 mg daily) alone. Patients who developed a BP ≥ 140/90 were treated with anti-hypertensives (HTN) and/or a mineralocorticoid antagonist (MA) prior to steroids. Hypokalemia was treated with supplementation or a MA. Patients with persistent or severe ME were initiated on prednisone (5 mg twice daily). To assess response to steroids, prednisone was added to AA at PSA progression. Therapy was continued until radiographic progression, toxicity, or withdrawal. Results: 60 patients were enrolled of whom 51 (83%) had metastases 16 (27%) received prior chemotherapy, 6 (10%) enzalutamide, and 4 (7%) ketoconazole. Grade (G) 3-4 adverse events (AEs) of interest included HTN (G3 n = 8, 13%; G4 n = 1, 2%), hypokalemia (G3 n = 4, 7%; G4 n = 0), fatigue (G3 n = 1, 2%; G4 n = 0). There was no G ≥3 edema. 9 patients (15%) initiated prednisone for toxicity: HTN (n = 3, 5%), hypokalemia (n = 4, 7%), fatigue (n = 2, 3%). Baseline PSA was 15.4 ng/mL. Time to nadir PSA was 2.5 months (IQR 1.4, 6.3) and median nadir PSA was 2.1 ng/mL. 67% of patients (n = 40) experienced a ≥50% PSA decline and 35% (n = 21) experienced a ≥90% decline. 19 patients (32%) initiated prednisone for PSA progression. Median time to prednisone initiation in patients with PSA progression was 6.1 months (IQR 4.9, 11.7); 5 patients (8.3%) had a PSA decline and 1 achieved a ≥50% decline. Levels of corticosteroids will be reported. Conclusions: In CRPC, AA without steroids is feasible, however clinically significant AEs, particularly HTN, can occur in a minority of patients. HTN and hypokalemia can be treated with anti-HTN agents or potassium without steroids in the majority. Use of AA without prednisone needs to be balanced with the potential risk of toxicity. Clinical trial information: NCT02025010.