The use of androgen receptor pathway inhibitors (ARPIs), such as abiraterone and enzalutamide, in combination with androgen deprivation therapy (ADT), has significantly enhanced outcomes in metastatic castration-sensitive prostate cancer (mCSPC). However, validated early prognostic markers to guide treatment decisions are still limited. The PSA Kelim Score, a simplified kinetic model based on PSA kinetics, may provide a practical method for early risk assessment.

We conducted a retrospective study of 146 high-volume mCSPC patients treated with abiraterone or enzalutamide plus ADT. The PSA Kelim Score, calculated from three PSA measurements within the first 100 days of therapy (PSA₃/PSA₁), was used to classify patients into favorable (< 1) or unfavorable (≥ 1) PSA kinetics. The primary endpoint was progression-free survival (PFS). Kaplan–Meier and Cox regression analyses were employed to assess the relationships between the PSA Kelim Score, treatment type, and survival outcomes.

Patients with favorable PSA kinetics (PSA Kelim Score < 1) experienced significantly longer median PFS compared to those with unfavorable PSA kinetics in both treatment groups (log-rank p < 0.001). Multivariate Cox analysis confirmed that unfavorable PSA kinetics (PSA Kelim Score ≥ 1) were independently associated with shorter PFS (HR = 2.10; 95% CI: 1.45–3.05; p < 0.001). No significant difference in PFS was observed between abiraterone and enzalutamide within each PSA Kelim subgroup.

The PSA Kelim Score seems to be a promising and practical prognostic biomarker in high-volume mCSPC. Early PSA decline (Kelim < 1) correlates with better outcomes, regardless of ARPI type. Incorporating it into clinical decision-making may allow for timely treatment adjustments. Prospective validation is needed.