Impact of Three-Month Androgen Deprivation Therapy on [68Ga]Ga-PSMA-11 PET/CT Indices in Men with Advanced Prostate Cancer—Results from a Pilot Prospective Study

SIMPLE SUMMARY: Positron emission tomography/computed tomography (PET/CT) with prostate-specific membrane antigen (PSMA)-specific tracers is gaining traction for prostate cancer imaging. The aim of this pilot study was to evaluate PSMA PET/CT imaging response in 30 patients who had undergone three months of androgen deprivation therapy (ADT). Different imaging indices and the modified PET response criteria in solid tumors 1.0 served as outcome measures. Most patients showed a consistent reduction of PSMA PET/CT indices over three months. A total of 24 (80%) participants were partial responders. Patients in the International Society of Urological Pathology grade group 5 (n = 16) showed a less prominent reduction of the imaging indices, and none of them reached a complete response. Collectively, our data support the clinical usefulness of PSMA PET/CT imaging for monitoring treatment response after the first three months of ADT. ABSTRACT: Purpose: The purpose of this pilot prospective study is to examine the gallium-68-prostate-specific membrane antigen-11 ([68Ga]Ga-PSMA-11) positron emission tomography/computed tomography (PET/CT) imaging response in patients with advanced or metastatic hormone-naïve prostate cancer (PC) after 3 months of androgen deprivation therapy (ADT). Methods: We prospectively included men with untreated, clinical stage III or IV PC scheduled to receive ADT for at least 6 months. [68Ga]Ga-PSMA-11 PET/CT images were obtained before the start of ADT and 10–14 weeks thereafter. The following indices were examined: maximum standardized uptake value (SUVmax), mean SUV, PSMA total volume, and PSMA total lesion values of the prostate, nodes, bones, and whole-body. The therapeutic response was assessed using the modified PET response criteria in solid tumors 1.0. A subgroup analysis of patients with the International Society of Urological Pathology (ISUP) grade group 5 versus <5 was also performed. Results: A total of 30 patients were eligible. All PSMA PET/CT indices were significantly reduced (p < 0.001) after 3 months of ADT. Twenty-four (80%) patients showed partial response. Complete response, stable disease, and disease progression were observed in two patients each. Sixteen patients with ISUP grade group 5 showed a less prominent SUVmax reduction (p = 0.006), and none of them reached complete response. Conclusions: Three months of ADT in patients with untreated, advanced PC significantly reduced PSMA PET/CT indices. While most participants partially responded to ADT, patients with ISUP grade group 5 showed a less prominent SUVmax reduction. Collectively, our pilot results indicate that [68Ga]Ga-PSMA-11 PET/CT imaging holds promise to monitor treatment response after the first three months of ADT.