Hierarchical Cluster Analysis of Cytokeratins and Stem Cell Expression Profiles of Canine Cutaneous Epithelial Tumors

The diagnosis of cutaneous epithelial tumors (CETs) in dogs is based on predominant histological differentiation patterns. However, the expression of a broad panel of antigens has not been comprehensively examined with immunohistochemistry. The present study aims to establish a comprehensive expression profile and identify useful diagnostic markers for each CET type. Cytokeratin (CK), stem cell, and other associated markers were immunohistochemically examined in 110 canine CETs. Among these, CK16 was useful for differentiating between basal and squamous cell carcinomas. Acantholytic squamous cell carcinomas were positive for CK8, CK18, and CK19, suggesting their close association with the apocrine duct. Unlike their benign counterparts, sebaceous carcinomas coexpressed CK5/6 and adipophilin. Smooth muscle actin (SMA) and p63 immunostaining were useful for accurately distinguishing between glandular and ductal differentiation in apocrine tumors. A case of apocrine carcinoma and malignant myoepithelioma was identified using anti-SMA antibodies. Stem cell expression profiles (CK8, CK15, CK19, and CD34) of hair follicle tumors were discrete and indicative of their anatomic origins. The effectiveness of immunohistochemistry for tumor diagnosis was further confirmed by hierarchical cluster analysis, through which selected markers were able to sort CETs into specific groups: CK5/6, CK8, CK14, CK16, CK18, CK19, p63, adipophilin, and SMA sorted tumors of epidermal, apocrine, or sebaceous origin; while CK8, CK14, CK15, CK16, CK19, CD34, and p63 sorted hair follicle tumors in agreement with their histological differentiation. In conclusion, the present study provides comprehensive immunohistochemical information, which could complement histomorphological features for the future classification of canine CETs.