Comparison of PSA Response to Generic Versus Innovator (Zytiga) Formulations of Abiraterone in Metastatic CRPC: A Retrospective Analysis

Abstract Introduction Abiraterone acetate has been shown to enhance overall survival and radiographic progression-free survival (rPFS) in men with metastatic castration-resistant prostate cancer (mCRPC). Presently, multiple generic brands of abiraterone are accessible in India. Nevertheless, evidence supporting the clinical equivalence of these generics when compared to the innovator has not been established, and thus, questions regarding their quality persist. Objectives This retrospective analysis aimed to compare the prostate-specific antigen (PSA) response in patients receiving generic or innovator (Zytiga) abiraterone for mCRPC. Materials and Methods This was a single-center, retrospective, comparative study. All relevant data from selected cases were collected from the hospital's electronic medical record (EMR). Patients with mCRPC, treated with either innovator or generic abiraterone from 2010 to 2019 and followed up until disease progression/death, were included. Patients who switched between generic and reference brands and vice versa were excluded. Patients in both arms were matched for prior treatment with docetaxel (yes/no), age at cancer diagnosis (>60, ≤60 years), and total Gleason's score (≥8, <8), in a ratio of 1:5. The primary outcome was to assess the difference in PSA nadir between the two study groups. Data were analyzed using Statistical Package for Social Sciences (SPSS) v.21 and GraphPad Prism 8.0.2. Results Out of the 114 patients enrolled, 10 patients received Zytiga (innovator), and the remaining received generic abiraterone. No statistically significant difference was observed in the median PSA nadir between the generic and innovator arms: 20.5 versus 88.5 ng/mL (p = 0.293). Patients in the generic group exhibited a similar median rPFS compared to the innovator group: 9.0 months (95% confidence interval [CI]: 6.68–11.31 months) versus 9.0 months (95% CI: 0–18.6 months), respectively (p = 0.539). The median time to PSA nadir was similar (3 months) between the two groups. The proportion of patients showing a PSA response at day 90 did not significantly differ between the two groups, with p = 0.38. The number of adverse events of any grade was comparable between the study groups, although grade 3/4 events were numerically higher in the generic group. Conclusion Generic abiraterone demonstrates a clinical response similar to that of Zytiga. Our findings strongly support the use of generic abiraterone in patients with mCRPC. The potential economic benefits of this substitution are substantial.