Prostate-specific membrane antigen (PSMA) is a type II transmembrane glycoprotein, which is heavily expressed in most prostate cancers. Immunohistochemistry (IHC) staining for PSMA is a long-established tool for pathologists in identifying prostate cancer, as well as a target for molecular imaging with PSMA-positron emission tomography (PET). This has generated considerable research interest in examining whether PSMA molecular expression as assessed with IHC is associated with clinical outcomes, or imaging findings. This is a pertinent clinical issue, as the adoption of PSMA-PET as the ‘gold standard’ for staging newly-diagnosed high-risk prostate cancer comes with a significant financial burden, with costs estimated at 1203 Australian dollars (AUD) per scan 1. Given that an estimated 4–10% of patients will not have a PSMA-avid lesion within the prostate 2, and its low sensitivity for detecting nodal disease in intermediate-risk patents 3, a significant number of resources are used on negative scans. PSMA IHC staining could therefore be a potential tool for predicting the presence of PSMA-PET-avid disease. It is widely available to pathologists and has a low cost per patient (30 AUD at our institution). To date, a number of studies have assessed PSMA IHC on and whole-mount radical prostatectomy specimens and consistently found associations between PSMA expression and PSMA-PET findings 4, 5. However, the correlation between IHC staining on biopsy cores and imaging findings is not as established, with few studies assessing this relationship 6, 7. We therefore undertook a retrospective audit of a prospectively collected database of our own biopsies to assess for a relationship between biopsy IHC and PSMA-PET findings. All transperineal biopsies conducted by a single surgeon (N. L. ) between November 2021 to July 2025 were scrutinised. A total of 222 transperineal prostate biopsies were taken in 197 individual patients. All patients had a template biopsy, with additional cognitive-fusion targeting of any Prostate Imaging-Reporting and Data System (PI-RADS) score ≥3 lesions, and/or any areas of focal avidity if a PSMA-PET was performed prior to initial biopsy. PSMA IHC was performed on patients with newly diagnosed prostate cancer with International Society of Urological Pathology Grade Group (ISUP GG) ≥2 or with ISUP GG 1 but high-risk features (three or more cores of ≥5 mm). PSMA-PET was routinely performed on all men with ISUP GG ≥2. In total, 74 men had PSMA IHC done on their biopsy specimens. IHC staining was performed on formalin-fixed, paraffin-embedded tissue, cut at 4 μm thickness. PSMA (clone ID6; NovaCastra/Leica, Nussloch, Germany) was used at 1: 50 dilution on a Benchmark Ultra autostainer (Ventana Medical Systems, Inc. , Tucson, AZ, USA) with OptiView diaminobenzidine (DAB) detection. All slides were reviewed by an experienced uropathologist (A. R. ) along with at least one other pathologist and assigned an ISUP GG. PSMA IHC was performed after the main clinical review and interpreted by a single pathologist (A. R. ). The core with the highest ISUP GG was utilised for IHC staining, as it was assumed to be most representative of the tumour. If multiple cores had the highest ISUP GG, the IHC staining was performed on the core with highest volume of tumour. Slides were assigned a visual IHC score from 1 to 3+ based on predominant PSMA expression patterns as quantified using a standard four-tiered visual scoring system (0 = negative, 1 + = weak, 2 + = moderate, 3 + = strong) 6 (Fig. 1). The PSMA-staining pattern was described as either luminal membrane, cytoplasmic, or both. A biopsy core was considered PSMA-PET concordant when there was a PSMA-PET-avid lesion (PRIMARY score ≥3) in the same anatomical location where clinically significant prostate cancer (ISUP GG ≥2) was found on a biopsy core. Patients with and without concordant lesions had their data compared, using the Mann–Whitney U tests. These tests were selected due to the non-normal distribution and ordinal nature of the data. Of the 74 patients who underwent PSMA IHC, 66 patients had PSMA-PET performed, with a median maximum standardised uptake value (SUVmax) of 6. 4. In all, 48/66 patients with a PSMA-PET showed a focal intraprostatic lesion (PRIMARY score ≥3) with a concordant positive biopsy core (Table S1). In three patients the highest IHC score was 1+, in 12 it was 2+, and in 58 it was 3+. One patient had no detectable PSMA staining. Based on the highest detected IHC score, patients that scored 3+ had a concordant lesion on their PSMA-PET 80. 1% of the time, whilst patients that scored 2+ had a concordant lesion on their PSMA-PET 41. 7% of the time. Patients that had concordant lesions on PSMA-PET demonstrated significantly increased IHC staining, pre-biopsy PSA, MRI PI-RADS score, and ISUP GG (Table S1). Measurements of highest IHC score were also significantly different between biopsy ISUP GGs (H4 = 13. 25, P = 0. 01), Kruskal–Wallis test). These results demonstrate that PSMA IHC expression on core biopsies is associated with both cancer ISUP GG, and imaging findings on PSMA-PET. This builds on prior studies, which demonstrated that PSMA IHC on transperineal prostate biopsy is strongly correlated with PSMA expression on whole-mount specimen pathology 7, and SUVmax on PSMA-PET 7. Other studies have demonstrated that PSMA expression on prostate biopsy and whole-mount pathology was associated with higher ISUP GG of disease, and higher rates of disease recurrence after radical prostatectomy 8. Our findings are consistent with these prior studies and demonstrate that stronger PSMA IHC staining on biopsy specimens is associated with increased rates of concordance with PSMA-PET findings, as well as increasing tumour ISUP GG. However, our study is significantly limited by its modest sample size, retrospective analysis and limited staining performed on only single cores by a single surgeon, limiting the interpretation of results. There is insufficient evidence to draw conclusions regarding the role PSMA IHC may play in selecting which patients may be benefit from PSMA-PET. However, our findings are consistent with previously published results, and PSMA staining on biopsy specimens seems to be correlated with whether the lesion will be avid on the PSMA-PET scan. Further research is required to assess the strength of this relationship, and the clinical utility of PSMA IHC as a tool at time of initial biopsy. This is an area that may benefit from further inquiry, as 4–10% of prostate cancers are not avid on PSMA-PET. Therefore, it may be worth investigating if PSMA IHC could be used to identify which patients may have PSMA-PET-avid disease, and any associated cost-benefits to improving patient selection for imaging. However, the clinical utility of this approach may be limited by intra-patient heterogeneity of PSMA expression through the tumour. Multiple studies have established that PSMA is expressed unevenly throughout tumours, affecting the accuracy of staining and impacting avidity on medical imaging 9, 10. This heterogeneity suggests that detailed staining and analysis of all biopsy cores may be superior to single-core analysis of the highest score, which we used in this study. Therefore larger, prospective studies are required to explore this issue and determine if PSMA IHC is a useful tool for identifying patients who may have avid disease on PSMA-PET, and if there is a cost-benefit to this approach. Ultimately, our data provides an early indication that this may be a fruitful approach, as we have found PSMA IHC staining to be associated with higher rates of concordance with PSMA-PET. Open access publishing facilitated by The University of Melbourne, as part of the Wiley - The University of Melbourne agreement via the Council of Australasian University Librarians. Jonathon Carll—This research was supported by the Commonwealth through an Australian Government Research Training Program Scholarship DOI: https: //doi. org/10. 82133/C42F-K220. Henry Yen-Cheng Pan—no conflicts exist to disclose. Nathan Lawrentschuk—proctor for both Robotic Surgery (Device Technologies Australia) and Focal Therapy with Nanoknife (Getz healthcare Australia). Andrew Ryan—No conflicts exist to disclose. The project involves retrospective analysis of existing clinical data. There was no direct participant contact or intervention. The study posed negligible risk to participants, and all data was de-identified prior to analysis. Therefore, a waiver of consent was obtained under the National Statement on Ethical Conduct in Human Research (NHMRC, 2025, Sections 2. 3. 9–2. 3. 12). Table S1. Data on patients that underwent PSMA IHC staining and PSMA-PET. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
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