PSMA PET/CT-Guided Multimodal Therapy for Pelvic Lymph Node Positive and De Novo Low-Volume Metastatic Prostate...

Background/Objectives: Metastatic prostate cancer is increasing in the Gulf Cooperation Council countries. This study presents a multimodal treatment protocol incorporating radiotherapy to primary and metastatic sites, guided by PSMA PET/CT, combined with systemic therapy for non-metastatic pelvic node-positive and de novo low-volume metastatic prostate cancer. Methods: We conducted a retrospective cohort study of patients treated with radical radiotherapy doses (68 Gy/25 Fr or 78 Gy/39 Fr) to the prostate gland and gross pelvic disease, and SBRT (35-40 Gy/5 Fr) to distant bone metastases. All patients received LHRH agonists ± abiraterone/prednisone or enzalutamide. Results: Twenty-four consecutive patients were analyzed. The median age was 70.1 years (IQR, 65.7-77.7), the median baseline PSA was 27.9 ng/mL (IQR = 19.7-53.8), and median follow up was 24 months (IQR = 20.4-31.2). Clinical staging was cT3b in (46%), cT2 in (25%), cT4 in (17%), cT3a in (13%) of patients. Pelvic nodal involvement (cN1) was present in 91.7% of patients, while 54.1% had metastatic disease. Treatment was well tolerated. Acute toxicity was predominantly grade 1 genitourinary (GU) toxicity, occurring in 87.5% of patients, with grade 2 GU toxicity observed in 8.2% and no acute gastrointestinal (GI) toxicity. Late toxicity remained minimal, with grade 1 and grade 2 GU toxicity reported in 45.8% and 4.2% of patients, respectively, and no late GI toxicity. Mild systemic treatment-related toxicities were reported in 25% of patients, including sexual dysfunction, hypokalemia, muscle weakness, osteoporosis and depression/anxiety. At the six-month follow-up PSMA PET/CT assessment, 85.7% achieved a complete metabolic response, and 14.2% achieved a partial response. Biochemically, 75% of patients achieved undetectable PSA levels (<0.01 ng/mL), with all patients achieving a PSA nadir < 0.2 ng/mL. Conclusions: This first, hypothesis-generating real-world experience from the GCC, suggests that an integrated approach combining systemic therapy with metastasis-directed therapy is feasible. Prospective randomized studies are required to validate these results.