P0427 - Localised Activation of the EMT Switch by Peri-Neural Invading Epithelial Cells in Prostate Cancer

Abstract: Introduction & Objectives: Invasion of the peri-neural space by malignant epithelial cell, known as Peri-neural Invasion (PNI), is an acknowledged prostate cancer (PCa) pathological feature associated with recurrence, increased risk of bone metastasis and poor survival. However the molecular mechanism underlying this pathology is relatively unknown. Here we assess the presentation of a metastatic phenotype by the peri-neural invading prostate epithelial cells, their spatial relationship to the tumour lesion and clinical outcome. Materials & Methods: FFPE blocks from an archival cohort (n=54) of radical prostatectomy patients, with associated full clinical history was retrieved under research ethics REC07/H1003/161+5 10_NOCL_02. Serial 4µm sections were stained using an automated multiplex TSA protocol on a Ventana Discovery platform for a panel of metastatic biomarkers (EphA2, pEphA2s897 , pMLC2, E-Cadherin, Vimentin, TOMM20, MTC01, NDUFB8, PTEN) along with the housekeeping landmark markers S100 (neural), pan-cytokeratin and DAPI. Slides were scanned on a Versa 3 platform with Halo image analysis. Prostate spatial zones were defined at 500µm intervals either side of the prostate capsule and pathological features were characterised. Univariate and multivariate (hierarchical clustering, UMap clustering) expression analysis and correlation with clinicopathological features was conducted within GraphPad Prism and R. Results: Marker expression analysis of the pooled (patient independent) PNI showed that all markers have significantly different expression levels dependent on their spatial location in relation to the prostate organ and tumour lesion (Kruskal Wallis p-value {$<$}2.2x10-16 except MCT01 (p=5.3x10-10)). Marker expression of amoeboid signalling (EphA2, pEphA2s897 , pMLC2) and mitochondrial defects (loss of Complex I/IV and gain of mitochondrial mass (TOMM20)), associated with a migrational switch to an activated metastatic phenotype in peri-neural invading epithelial cells in PNI close to the prostate edge but outside the tumour lesion correlates with a reduction in overall survival of 28 months (119 months 95%CI 0.3572-1.835 vs 147 months 95% CI 0.5451-2.8; p=0.0249). Conclusions: Peri-neural invading epithelial cells close to the edge of the prostate have features consistent with a switch metastatic behaviour in contrast to the tumour embedded peri-neural invading epithelial cells. This switch was associated with a significant reduction in overall survival.