Vet Pathol 36:601–603 (1999) BRIEF COMMUNICATIONS and CASE REPORTS Secretory Carcinoma of the Canine Mammary Gland

Abstract. Secretory carcinoma is an uncommon variant of breast cancer, characterized by the presence of intracellular and extracellular eosinophilic secretion. Here, we report the cytologic, histologic, and immunohis-tochemical findings of a secretory carcinoma diagnosed in the left inguinal mammary gland of a 3-year-old female German Shepherd Dog. The fine-needle aspiration cytology showed numerous large branching sheets of neoplastic cells and isolated cells with cytoplasmic vacuoles. Histologically, the tumor was composed of cells with clear cytoplasm and prominent vacuoles that pushed the nuclei to the periphery, resembling signet ring cells. These cells were arranged in solid or tubular structures with lumenal spaces filled with eosinophilic secretion. Immunohistochemical reactions to cytokeratin (CAM 5.2) and -lactalbumin were strongly positive in all neoplastic cells, and staining for vimentin and S100 protein was negative. The cytomorphologic and immunohistochemical features of this tumor are similar to those seen in tumors in women, hence enabling the diagnosis of a rare case of primary secretory carcinoma of the canine mammary gland. Key words: Dogs; mammary carcinoma; mammary gland; secretory carcinoma. Secretory carcinoma is a rare variant of primary mam-mary tumor in humans characterized histologically by the presence of large amounts of intra- and extracellular secre