KELIM PSA as a Prognostic Biomarker in Castration-Resistant Prostate Cancer Treated with ARPI

<b>Background/Objectives:</b> Prostate cancer is a leading cause of cancer-related morbidity and mortality. While prostate-specific antigen (PSA) is crucial for monitoring, its static levels are limited in predicting outcomes precisely. The Kinetics of Elimination of PSA (KELIM PSA) has recently emerged as a dynamic biomarker of treatment response. This research sought to determine the predictive power of KELIM PSA in castration-resistant prostate cancer (CRPC) on androgen receptor pathway inhibitors (ARPI). <b>Methods:</b> This study retrospectively analyzed 98 CRPC patients treated with enzalutamide or abiraterone. The patients were categorized as either unfavorable (KELIM < 1) or favorable (KELIM ≥ 1). Demographic and clinical characteristics were compared, and survival outcomes were evaluated using Kaplan-Meier curves and Cox regression. <b>Results:</b> Of the cohort, 42 (42.9%) patients had favorable and 56 (57.1%) unfavorable KELIM values. The unfavorable group had a higher mortality rate (62.5% vs. 38.1%, <i>p</i> = 0.029). Univariate analysis showed that poor KELIM results increased mortality risk twofold (hazard ratio [HR]: 2.30, 95% confidence interval [CI]: 1.26-4.19, <i>p</i> = 0.006). In multivariable analysis, unfavorable KELIM remained independently associated with worse overall survival (HR: 2.09, 95% CI: 1.12-3.89, <i>p</i> = 0.020), together with second-line ARPI (HR: 3.19, 95% CI: 1.71-5.93, <i>p</i> < 0.001) and ADT + docetaxel during CSPC (HR: 2.14, 95% CI: 1.11-4.12, <i>p</i> = 0.022). Kaplan-Meier curves revealed that the unfavorable group had notably reduced overall survival and progression-free survival (log-rank <i>p</i> = 0.018). <b>Conclusions:</b> KELIM PSA is an independent predictor in ARPI-treated CRPC. By integrating PSA kinetics into prognostic models, risk stratification may be improved, and this may guide individualized treatment. Prospective multicenter validation is warranted.