Triple-negative mammary carcinoma in two male dogs.

Triple-negative tumors are characterized immunohistochemically by the absence of positivity to sex hormone receptors and to human epidermal growth factor receptor 2. Additionally, they are differentiated into basal-like and non-basal (or null) subtypes, based on the presence of basal cytokeratin expression (CK5/6, 14, and17). Triple-negative subtypes are yet to be characterized in male dogs, to our knowledge. We report herein the clinical and pathologic findings and molecular characterization of carcinoma in the mammary glands of 2 male dogs. Case 1 was diagnosed as a grade II tubulopapillary carcinoma; case 2 was diagnosed as a grade II carcinoma in a mixed tumor. The tumors were characterized phenotypically as triple-negative basal and triple-negative non-basal, respectively.