Early Evaluation of PSA Response in Metastatic Prostate Cancer Treated with Abiraterone

Abstract

Background: According to the main prostate cancer guidelines, the response to treatment with abiraterone plus prednisone (AA+P) must be evaluated by assessing prostate-specific antigen (PSA) levels at 12 weeks. Recent studies have shown that early PSA decline, at 4 weeks, maybe a surrogate marker for survival. The objective of this work was to analyze if a decline in PSA at 4 weeks correlates with a better outcome in terms of OS (overall survival) and PFS (progression-free survival). Methods: We evaluated 168 patients (with a median age of 71 years) with prostate cancer who had started AA+P treatment between February 2012 and July 2019. Patients were divided into three different groups according to the decline of PSA (≥30%, ≥50%, and ≥90%) at 4, 8, and 12 weeks. Statistical survival analysis was performed using the Kaplan-Meier method. Results: After a follow-up of 69 months, a PSA decline ≥ 30% at 4 weeks was associated with longer median OS times (28 vs. 18 months; p = 0.027). A decline in PSA by ≥50% was also associated with increased median OS times (36 vs. 21; p = 0.003). Cox univariable analysis indicated that a decrease in PSA (both by ≥30% and ≥50) were predictive of OS at 4 weeks (PSA ≥ 30%: HR = 1.568, 95%CI [1.041, 2.360], p = 0.031; PSA ≥ 50%: HR = 1.901, 95% CI [1.222, 2.956], p = 0.004); although multivariable analysis did not confirm these results. The prior administration of chemotherapy was an independent risk factor for death (HR = 2.511; p < 0.001) and progression (HR = 3.238; p < 0.001), probably because of different factors. Conclusion: A decrease in PSA by ≥30% or ≥50% at 4 weeks after starting treatment with AA+P correlated with longer PFS and OS, and provides clinically meaningful information guiding the physicians towards a personalized treatment.