Abstract A064: Identification and phenotypical evaluation of androgen receptor indifferent phenotype in treatment-naïve primary prostate cancer cases

Abstract INTRODUCTION: High-grade, locally advanced primary prostate cancer (PC) carries an increased risk of metastatic progression. The Androgen Receptor indifferent (ARi) phenotype is characterized by low PSA expression despite high expression of AR and has been noted in CRPC where it is considered to be induced by treatment. We sought to examine primary, treatment-naïve PC cases for evidence of ARi. METHODS: We applied digital pathology and multiplexed, single-cell resolution tissue staining techniques to a locally advanced PC patient cohort with 27 patients, and computational RNA expression analysis to the TCGA prostate cancer dataset (TCGA-PRAD). Thus, we first quantify AR and PSA protein expression levels in cells and then identify tissue regions with >30% AR+ cells and