This study analyzed and compared the spatial distribution and level of ERα expression in the benign and malignant prostatic tissue of men and dogs using immunohistochemistry (IHC) and assessed the suitability of dogs as a model to further understand the role of ERα in human PCa.<h4>Methods</h4>Formalin-fixed paraffin-embedded (FFPE) human (n = 146) and canine (n = 61) prostatic tissue specimens were analyzed immunohistochemically for ERα expression using a monoclonal anti-human ERα antibody, previously validated for cross-reactivity with canine tissue. This evidence concerns the gene ESR1 and posterior cortical atrophy.