PSMA PET vs. pelvic MRI in biochemically recurrent prostate cancer.
Authors: Sonni Ida , Murthy Vishnu , Mehta Raj , Chung Alex , Unterrainer Lena , Hotta Masatoshi , Farolfi Andrea , Benitez Cecil , Armstrong Wesley Robert , Doddipalli Sahith , Bandara Anishka , Valle Luca , Kishan Amar Upadhyaya , Benz Matthias R. , Raman Steven 
Published: February 2025

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Background:
After primary definitive therapy of localized prostate cancer with either radical prostatectomy or radiation therapy, up to 50% of patients will experience biochemical recurrence (BCR) of disease. The objective of this descriptive, retrospective analysis is to compare the performance of PSMA PET/CT and pelvic MRI in BCR and investigate the added value of their combined use in this patient population.
Methods:
Patients with BCR who underwent PSMA PET/CT and pelvic MRI within three months of each other at the University of California, Los Angeles with available imaging and follow-up data were included in our retrospective analysis. Two board-certified nuclear medicine physicians blinded to clinical information interpreted the PSMA PET/CT scans independently and described up to three positive findings. A third nuclear medicine physician resolved any disagreements (2:1 majority rule). In a similar framework, two radiologists interpreted the pelvic MRIs with a third radiologist serving as a tiebreaker. For patients with metastatic disease, PSMA PET/CT scans were interpreted according to PROMISE criteria. Data on disagreements between clinical PSMA PET/CT and pelvic MRI reads, disagreements between blinded and clinical PSMA PET/CT and pelvic MRI reads, and subsequent management based on findings from clinical PSMA PET/CT and pelvic MRI were collected.
Results:
101 patients were included in this retrospective analysis, of which 84 (83%) had localized BCR and 17 (17%) had metastatic BCR. 10/84 (12%) patients with localized BCR had a negative clinical pelvic MRI and positive PSMA PET/CT, with 33% of these lesions noted to be in the lymph nodes, while 8/84 (10%) patients had a negative clinical PSMA PET/CT and positive pelvic MRI, with 100% of these lesions noted to be in the prostate or prostate bed. 12/17 (71%) patients with metastatic BCR had a positive clinical PSMA PET/CT and negative pelvic MRI. In 10/84 (12%) patients with localized BCR, the blinded PSMA PET/CT reads were negative while the clinical PSMA PET/CT reads were positive, and in 7/84 (8%) patients, the blinded pelvic MRI reads were negative while the clinical pelvic MRI reads were positive. In 2/17 (12%) patients with metastatic BCR, the blinded PSMA PET/CT reads were negative while the clinical PSMA PET/CT reads were positive, and in 1/17 (6%) patients, the blinded pelvic MRI reads were negative while the clinical pelvic MRI reads were positive. 48% of patients underwent radiation as a next step in management, 26% underwent biopsy, 15% underwent follow-up imaging, and 11% underwent other focal or systemic therapy.
Conclusions:
In this retrospective, descriptive analysis, there was good agreement between PSMA PET/CT and pelvic MRI for localized BCR, although pelvic MRI may overcall lesions in the prostate and prostate bed and miss nodal metastases. For patients with metastatic BCR, PSMA PET can disclose lesions that are outside the field-of-view of pelvic MRI.