Immunohistochemical and histopathological validation of 18F‐PSMA‐1007 PET/CT for intraprostatic cancerous lesions

Abstract Introduction Prostate‐specific membrane antigen (PSMA) is overexpressed in prostate cancer (PCa). In this study, we aim to immunohistochemically and histopathological validate the fluorine‐18 ( 18 F)‐PSMA‐1007 positron emission tomography/computed tomography (PET/CT) for intraprostatic PCa lesions. Methods Between February 2019 and October 2020, patients with biopsy‐proven, treatment‐naïve intermediate‐to‐high‐risk PCa undergoing an 18 F‐PSMA‐1007 PET/CT before robot‐assisted radical prostatectomy (RARP) were prospectively enrolled. For all PCa lesions found on whole‐mount histopathology, location, size, International Society of Urological Pathology (ISUP) grade group (GG), and immune reactive score (IRS) were assessed after PSMA staining. ISUP GG ≥ 3 PCa was defined as clinically significant (cs) PCa. All lesions were matched on PSMA PET/CT and the maximum standardized uptake value (SUVmax) was measured. Results A total of 125 lesions were analyzed in the 80 RARP specimens, of which 49 (40%) were csPCa and 76 (60%) non‐csPCa. Linear multivariable regressions showed that an increase in SUVmax significantly correlated with a higher ISUP GG ( p values between 0.021 and 0.001) and a higher IRS ( p = 0.017). Logistic multivariable regression showed that csPCa significantly correlated with a higher SUVmax (odds ratio, OR: 1.17 95% confidence interval, CI: 1.04–1.21, p = 0.005), an increase in tumor length (OR: 1.05 95% CI 1.01–1.10, p = 0.020) and a higher IRS (OR; 1.24 95% CI 1.07–1.47, p = 0.006). A SUVmax threshold of 4 would have resulted in one (2%) missed lesion with csPCa. Conclusion This prospective study revealed that 18 F‐PSMA‐1007 PET/CT SUVmax is correlated with the ISUP GG and IRS, and thereby could be a tool to characterize intraprostatic PCa lesions.