Canine inflammatory mammary carcinoma: histopathology, immunohistochemistry and clinical implications of 21 cases.

Human inflammatory breast carcinoma (IBC) is the most malignant type of breast cancer with an extremely poor prognosis. The dog is the unique animal species in which spontaneous inflammatory mammary carcinoma (IC) has been reported, although it is not well documented. The purpose of this study was to characterize histopathologically and immunohistochemically the canine IC, considering associated clinical features. Twenty-one dogs diagnosed with IC and with known clinical and necropsy data were included in the study. Tissue samples from necropsies underwent a histopathological review and an immunohistochemical study (Ki-67, estrogen receptor (ER), progesterone receptor (PR), and P53 tumor suppressor protein). The histological study revealed several types of carcinomas (solid, tubular, papillary, and adenosquamous) and three lipid-rich carcinomas. All tumors were ER negative. Two histological patterns of neoplastic dermal infiltration were observed: tubular/papillary and sarcomatous-like. Dermal sarcomatous-like infiltration was significantly related to previous treatments with progestagens (p = 0.006), primary type of IC (p = 0.03), extreme local pain (p = 0.02), reduced observation of emboli in dermal lymphatic vessels (p = 0.01), and increased expression of p53 (p = 0.001). PR expression was significantly higher in secondary post-surgical IC (p = 0.04). The absence of PR was related to the existence of pulmonary metastases at necropsy (p = 0.04). Canine primary IC is the most aggressive form of this disease with distinct histopathological and immunohistochemical characteristics. Progestins and endocrine-related mechanisms seem to be involved in canine IC development. Canine IC could serve as a spontaneous model for human IBC, particularly in studies concerned with new therapeutics approaches.