Histomorphological features and ezrin expression in testicular seminomas in dogs: an association with potential prognostic value

Seminoma (SEM) is one of the most frequent testicular neoplasms in dogs, originating from germ cell lineage of the seminiferous tubule and divided into diffuse and intratubular patterns, according to location. Periodic acid-Schiff (PAS) staining is used to classify human SEMs but there is no consensus regarding canine SEMs. Ezrin expression has been detected in several human neoplasms and is linked to a poor prognosis. However, its expression in testicular tumours is rarely described in human SEMs and no similar study was found in dogs. This study aimed to evaluate the presence of ezrin by immunohistochemical labelling and PAS staining in canine SEM samples, correlating them with histomorphological features. Twenty-three canine SEMs were subjected to PAS staining and anti-ezrin immunohistochemical analysis. Pink-magenta-stained samples were PAS positive. Percentage of ezrin immunolabelled positive cells, immunolabelling intensity and ezrin location were recorded. Intratubular SEMs were PAS positive but diffuse samples were PAS negative. Twenty cases (87%) were ezrin positive by cytoplasmic immunolabelling. Ezrin immunolabelling intensity was heterogeneous among tumour samples, similar to normal testicular tissue, but with different locations in each case. The percentage of positive cells was high in 18 cases and correlated positively with diffuse SEM. Ezrin immunolabelling correlated with cytoplasmic immunolocalisation, intensity and percentage of immunolabelled cells. This study confirmed differences in PAS staining for canine SEM patterns and ezrin immunolabelling in diffuse and intratubular canine SEMs, demonstrating ezrin's potential role in this testicular tumour in dogs. Diffuse canine SEM had local invasive features associated with ezrin immunolabelling. According to these findings, PAS staining correlates with canine SEM histomorphology and ezrin immunolabelling can be used as a biological marker of the local invasiveness potential of canine SEMs.