Impact of Absolute PSA Value and Relative PSA Response Rate on Overall Survival in Patients With Metastatic Castration‐Sensitive Prostate Cancer Treated With Androgen Receptor Signaling Inhibitors

BACKGROUND: Although the relationship between prostate-specific antigen (PSA) kinetics and prognosis in metastatic castration-sensitive prostate cancer (mCSPC) cases has been examined in a pivotal randomized control trial and real-world studies, there are no known reports regarding which PSA kinetic parameter is the most valuable surrogate marker for indicating survival outcome. The present retrospective multicenter study investigated the relationship of absolute PSA value and relative PSA response rate with the prognosis of mCSPC patients in real-world clinical settings. METHODS: Among patients diagnosed with mCSPC, 114 who received androgen receptor signaling inhibitors (ARSI) between June 2019 and September 2024 were included. Outcome measures included achievement of absolute PSA value and relative PSA response at 3 months following initiation of first-line ARSI treatment, survival outcome. RESULTS: The median follow-up period was 20 months. The results were insufficient to demonstrate a difference in terms of Overall survival (OS) stratified by achievement of PSA ≤ 0.2 ng/mL (hazard ratio [HR] 0.44, 95% confidence interval [CI] 0.16-1.23; p = 0.119). Nevertheless, patients who achieved a ≥ 99% decline in PSA showed significantly better OS as compared with those who did not (HR 0.27, 95% CI 0.10-0.74; p = 0.011). After adjustment for liver metastasis and EOD ≥ 3, achievement of PSA decline ≥ 99% was associated with better OS (HR = 0.17, 95% CI 0.05-0.62; p = 0.007). CONCLUSIONS: These results show the usefulness of PSA decline ≥ 99% as a prognostic marker for mCSPC patients.