Improved specificity with 68Ga PSMA PET/CT to detect clinically significant lesions “invisible” on multiparametric MRI of the prostate: a single institution comparative analysis with radical prostatectomy histology

Purpose: Positron emission tomography (PET) for prostate-specific membrane antigen (PSMA) represents a promising method for prostate cancer diagnosis and staging. Comparisons of PSMA-based tumour characterisation to multiparametric MRI (mpMRI) are limited, hence this study sought to compare the diagnostic accuracy of Ga-PSMA PET/CT to mpMRI against radical prostatectomy (RP) whole gland histopathology. Methods: A retrospective cohort study of consecutive patients who underwent pre-operative mpMRI and Ga-PSMA PET/CT followed by a RP was performed. Standard clinical parameters were collected. “Per patient” and “per lesion” analyses for image-based detection according to RP histopathology were described using sensitivity, specificity and other measures of diagnostic accuracy. Results: Fifty-eight patients (median age 65.5\ua0years, median PSA 7.35\ua0ng/mL) underwent RP, resulting in a high-risk cohort (≥pT3 69%). Sensitivities for identification of index lesion, bilateral and multifocal disease were 90%, 21%, 19% for mpMRI and 93%, 42%, 34% for Ga-PSMA PET/CT. Histology analyses revealed 88 cancer foci of Gleason grades 3 + 3 (4%), 3 + 4 (64%), 4 + 3 (19%), 4 + 4 (3%) and ≥ 4 + 5 (10%), of which Ga-PSMA PET/CT correctly detected more foci (78%, AUC 0.817) than mpMRI (69%, AUC 0.729). Conclusions: Ga-PSMA PET/CT may better reflect RP histopathology compared to mpMRI when considering multifocal and bilateral disease. These findings may influence surgical planning, targeted biopsy and focal therapy strategies and require further research