Localized activation of the metastatic phenotype within the perineural region in prostate cancer

253 Background: Perineural Invasion (PNI) is defined as malignant epithelial cell invasion of the perineural space and nerves. Despite widespread acknowledgement of the clinical significance of PNI as a PCa pathological finding associated with recurrence, increased risk of bone metastasis and poor survival, the molecular mechanism underlying this pathology is relatively unknown. The malignant epithelial cells within the PNI potentially provides a spatially defined “snapshot” of disease progression, as the cells switch to a more migrational phenotype associated with metastatic progression. Here we present the initial spatial PNI phenotypic characterisation in PCa. Methods: Archival FFPE blocks, with associated full clinical history, from patients who underwent a radical prostatectomy for prostate cancer were retrieved under research ethics REC#07/H1003/161+5 10_NOCL_02. Biomarkers EphA2, pEphA2s897, pMLC2, E-Cadherin, Vimentin, TOMM20, MTC01, NDUFB8, PTEN were assessed on 4µm serial sections stained using a multiplex TSA protocol, with S100, pan-cytokeratin and DAPI acting as landmarks, on a Ventana Discovery platform prior to scanning on a Versa 3 platform with Halo image analysis. Prostate zones were defined at 500µm intervals either side of the prostate capsule. Univariate and multivariate (hierarchical clustering, UMap clustering) expression analysis and correlation with clinic-pathological features was conducted within R. Results: The PNI epithelial cells within each spatial zone of the prostate are significantly different to each other (Kruskal-Wallis test p < 2.2x10−16 except for MTC01 p = 5.3x10−10). In comparison with the local tumour lesion, PNI epithelial cells localised within 1000µm of the prostate edge and outside the tumour lesion, have undergone a migrational switch, gaining features associated with an activated metastatic phenotype, with increased expression of amoeboid signalling (EphA2, pEphA2s897, pMLC2) and mitochondrial defects (loss of Complex I and IV, gain of mitochondrial mass (TOMM20)). Patients clustering by multivariate expression trends across the prostate regions showed 4 distinct patient groups, with PNI epithelial cells in patient group 1 & 2 displaying a more epithelial to mesenchymal (EMT) phenotype, especially in the first 1000µm inside the prostate organ. Conclusions: Cells within PNI close to the edge of the prostate have features consistent with a switch to migrational/metastatic activation in contrast to the more indolent cell type found deeper within the tumour. Further characterisation of this localised migrational upregulation will help in understanding the transition from a localised to a metastatic phenotype.