Quantification of PSMA expression via PSMA PET is well-established, however quantification of PSMA via immunohistochemistry (IHC) is not standardized. Our aim was to determine the most optimal PSMA IHC scoring system to quantify PSMA expression with PSMA PET as reference standard.
Primary intermediate- and high-risk prostate cancer patients received an [18F]PSMA-1007 PET/MRI followed by radical prostatectomy. SUVmax, SUVmean and Ki of the prostate tumor was determined. Prostate tumors were stained with anti-PSMA antibodies and scored by 2 readers via 10 IHC scoring systems: histochemical score (H-score), immunoreactivity scorepredominant intensity (IRSpredominant intensity), IRS classificationpredominant intensity, IRSmean intensity, IRS classificationmean intensity, Allred score, predominant expression pattern, Shannon diversity index (SDI), percentage negatively stained cells and total percentage positively stained cells. Spearman's rank correlation coefficients (ρ) were calculated between PET parameters and IHC scoring systems. Interreader agreement for the IHC scoring systems was measured by the intraclass correlation coefficient (ICC).
Fifty tumors in 46 patients were analysed. H-score had the best correlation with SUVmax (ρ 0.615 p < 0.0001) and SUVmean (ρ 0.570, p < 0.0001) and the second best correlation with Ki (ρ 0.411, p = 0.0030). SDI had the best correlation with Ki (ρ -0.440, p = 0.0014) and the second best correlation with SUVmax (ρ -0.516, p = 0.0001) and SUVmean (ρ -0.490, p = 0.0003). A moderate interreader agreement was observed for H-score (ICC 0.663, 95% CI 0.495-0.797) and SDI (ICC 0.546, 95% CI 0.354-0.725).
H-score had the best correlation with PSMA PET quantification and an acceptable interreader agreement. Therefore, we deem H-score the most optimal PSMA IHC scoring system.
European journal of nuclear medicine and molecular imaging. 2024 Sep 13 [Epub ahead of print]
Niloefar Ahmadi Bidakhvidi, Thomas Gevaert, Maxim De Schepper, Marcella Baldewijns, Enrique Havinga, Wies Deckers, Annouschka Laenen, Gaëtan Devos, Alexander Giesen, Steven Joniau, Michel Koole, Wouter Everaerts, Christophe M Deroose, Karolien Goffin
Nuclear Medicine, University Hospitals Leuven, Leuven, Belgium., Urogenital, Abdominal and Plastic Surgery, Department of Development and Regeneration, KU Leuven, Leuven, Belgium., Pathology, University Hospitals Leuven, Leuven, Belgium., Radiology, University Hospitals Leuven, Leuven, Belgium., Interuniversity Institute for Biostatistics and Statistical Bioinformatics, Leuven, Belgium., Urology, University Hospitals Leuven, Leuven, Belgium., Nuclear Medicine, University Hospitals Leuven, Leuven, Belgium. .