Head-to-Head 18F-rhPSMA-7.3 and 18F-PSMA-1007 PET/CT in Recurrent Prostate Cancer: Pulmonary and Nodal Uptake as a Diagnostic Challenge

This report presents a within-patient comparison of 18F-rhPSMA-7.3 and 18F-PSMA-1007 PET/CT in a 71-year-old man with Gleason score 4 + 3 = 7, pT3bN1 metastatic castration-resistant prostate cancer after robot-assisted radical prostatectomy, multiple androgen-deprivation and androgen receptor-directed treatments, and radiotherapy for para-aortic nodal metastases. The scans showed concordant PSMA-avid cervical-to-mediastinal lymphadenopathy and an ill-defined right lower-lobe pulmonary lesion with a recorded SUVmax > 15, despite distinct physiologic biodistributions. Infection or inflammation remained a relevant differential diagnosis, and the patient declined biopsy. Antibiotics did not improve the CT findings. After enrollment in a clinical trial of systemic therapy, the last available pretreatment prostate-specific antigen (PSA) level of 42.4 ng/mL decreased to 3.1 ng/mL, with marked disease regression. The concordant dual-tracer findings, lack of response to antibiotics, and subsequent radiographic and biochemical response to systemic therapy favored nodal and pulmonary metastases from prostate cancer. However, without histopathologic confirmation, the diagnosis remains presumptive, highlighting the need to integrate PET biodistribution, semiquantitative uptake, anatomic imaging, and longitudinal clinical findings.