Prostate Specific Membrane Antigen Targeted Positron Emission Tomography of Primary Prostate Cancer: Assessing Accuracy with Whole Mount Pathology

Purpose: We evaluated which lesions are detected and missed on [Ga-68]Ga-PSMA (prostate specific membrane antigen)-11 positron emission tomography in patients with primary prostate cancer. Materials and Methods: Patients undergoing radical prostatectomy were enrolled in this prospective observational study. Patients underwent [Ga-68] Ga-PSMA-11 positron emission tomography/computerized tomography or positron emission tomography/magnetic resonance imaging prior to surgery and received a dose of [Ga-68] Ga-PSMA-11 intraoperatively for positron emission tomography of extirpated specimens. Whole mount pathology was performed with lesion and intralesion based analysis to determine the characteristics of lesions detected or not detected by PSMA positron emission tomography. Lesion volume was determined by planimetry and clinically significant lesion volume was calculated as lesion volume x fraction pattern 4/5. Results: On whole mount analysis 30 cancerous lesions were found in a total of 15 patients, including 4, 15, 4, 1 and 6 which were Grade Group 1, 2, 3, 4 and 5, respectively. PSMA-positron emission tomography detected 100% of primary/index lesions and 8 of 11 (82%) secondary lesions. All Grade Group 3-5 lesions were detected vs 12 of 15 Grade Group 2 lesions. When comparing Grade Group 2 vs 3-5, lesion size was similar (p = 0.48) but the standardized uptake value was lower for Grade Group 2 vs 3-5 (5.3 vs 7.9, p = 0.03). The 3 missed lesions showed 10% or less of pattern 4 and a Gleason pattern 4/5 volume of less than 0.1 cm(3). Conclusions: PSMA positron emission tomography detected 100% of primary/index lesions in this study. The 3 missed secondary lesions were small and had a low percent of pattern 4. This argues for further study to better understand what defines clinically significant prostate cancer, which would assist in determining whether small lesions that become challenging to detect by [Ga-68]Ga-PSMA-11 positron emission tomography confer a risk to the patient.