BACKGROUND AND OBJECTIVE: In prostate cancer treated with androgen deprivation therapy (ADT), the initial sign of treatment resistance is often prostate-specific antigen (PSA) progression, followed by radiographic progression. However, the association between these two forms of progression remains unclear, especially in patients with metastatic castration-sensitive prostate cancer (mCSPC) treated with androgen receptor pathway inhibitors. We sought to evaluate the association between radiographic progression, PSA progression, and outcomes of apalutamide therapy in mCSPC. METHODS: We analyzed individual participant-level data for patients randomized within the TITAN trial who experienced radiographic progression during follow-up (N = 326). This study investigated radiographic progression without simultaneous or preceding PSA progression, as defined by the Prostate Cancer Working Group 2 (discordant progression), and explored the association of such progression with radiographic progression-free survival. KEY FINDINGS AND LIMITATIONS: Among the patients who developed radiographic progression, 115 (35.3%) had been treated with apalutamide plus ADT (the apalutamide group) and 211 (64.7%) with placebo plus ADT (the placebo group). Discordant progression occurred in 52.2% of patients (60 of 115) in the apalutamide group and 27.5% (58 of 211) in the placebo group (p < 0.001). A multivariable logistic regression analysis showed that discordant progression was associated with apalutamide treatment. We found evidence of an association between discordant progression and shorter radiographic progression-free survival. CONCLUSIONS AND CLINICAL IMPLICATIONS: This study found that nearly half of the patients with mCSPC treated with apalutamide who experienced radiographic progression developed it without corresponding PSA progression, suggesting that heavy reliance on PSA monitoring may be inadequate for assessing disease activity in this context. PATIENT SUMMARY: In patients who have metastatic castration-sensitive prostate cancer (mCSPC) and are being treated with apalutamide, radiographic images may show cancer progression even if prostate-specific antigen tests indicate no change. This highlights the importance of regular imaging when using apalutamide to manage mCSPC.

Department of Urology Comprehensive Cancer Center Medical University of Vienna Vienna Austria; Department of Urology Medical University of Silesia Zabrze Poland

Department of Urology Comprehensive Cancer Center Medical University of Vienna Vienna Austria; Department of Urology Weill Cornell Medical College New York NY USA; Department of Urology University of Texas Southwestern Dallas TX USA; Karl Landsteiner Institute of Urology and Andrology Vienna Austria; Department of Urology 2nd Faculty of Medicine Charles University Prague Czech Republic

Department of Urology The Jikei University School of Medicine Tokyo Japan

Department of Urology Vita Salute San Raffaele University Milan Italy

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