The Blind Spot of PSMA-PET Staging? Intraductal Carcinoma of the Prostate Is Overrepresented in Patients With No Uptake Pattern on Prostate-Specific Membrane Antigen Positron Emission Tomography and High-Grade Prostate Cancer

Prostate-specific membrane antigen positron emission tomography (PSMA PET) is increasingly used to diagnose and stage prostate cancer. A PRIMARY score uses anatomical localization and uptake patterns to improve diagnostic accuracy. We evaluated the histopathology of patients with no uptake pattern (PRIMARY score 1) and the prevalence of intraductal carcinoma of the prostate (IDC-P) in this subset compared with those with an uptake pattern (PRIMARY score ≥ 2). A 2-center, retrospective cohort study was conducted including consecutive patients imaged with intraprostatic [68Ga]Ga-PSMA-11 or [18F]DCFPyL PSMA PET before radical prostatectomy. All PSMA PET scans were centrally reviewed by nuclear medicine physicians, with PRIMARY scores and quantitative imaging parameters recorded. Perioperative characteristics, Prostate Imaging Reporting and Data System (PI-RADS), and histopathology were collected. The distribution of grade group and other histopathological findings, including IDC-P, were examined according to PSMA uptake patterns. A total of 178 patients were analyzed. A PRIMARY score 1 finding on intraprostatic PSMA PET was seen in 30 (17%) patients. IDC-P in prostatectomy specimens was more frequent in these patients compared with PRIMARY score ≥ 2 patients (12/30, 40% vs 31/148, 21%; P = .026). In the PRIMARY score 1 subset, patients with IDC-P had considerably more pathological grade group ≥ 3 disease than those without IDC-P (100% vs 33%). Eighty-one percent of all patients had PI-RADS scores 4 or 5 on prebiopsy MRI. This study is potentially limited by the selection of patients with PRIMARY score 1 disease who subsequently proceeded to surgery. In patients who are being considered for radical prostatectomy because of adverse clinical, PI-RADS or biopsy features, a PSMA PET demonstrating no intraprostatic uptake pattern should not be considered inherently a marker or small volume or lesser grade disease. Some high-grade cancers, particularly those associated with IDC-P, may not be well visualized on PSMA PET.