A case of feline primary inflammatory mammary carcinoma: clinicopathological and immunohistochemical findings.

The clinicopathological and immunohistochemical findings of a primary feline mammary tumour with features similar to human and canine primary inflammatory carcinoma are described for the first time. The cat presented to the clinic for the rapid onset of oedema, severe erythema, local pain and warmth of the inguinal region, with a pustular-to-nodular cutaneous lesion in association with an ill-defined underlying mass. An epithelial malignant tumour was diagnosed by cytological investigation. Necropsy revealed a thickening of the skin with oedema of the subcutis in the right inguinal area, and regional and distant metastases. Histology showed an unencapsulated tubulopapillary proliferation of malignant epithelial cells, with a massive embolisation in the dermal lymphatics and a mild inflammatory infiltrate. Through immunohistochemistry, the tumour was found to be oestrogen (ER)-alpha-, androgen (AR)- and progesterone (PR)-negative; neoplastic cells were ER-alpha, AR-negative and focally PR-positive. An irregular, mild and focal HER-2 immunoreactivity was present (score +1, non-HER-2 overexpressing). The neoplastic cells were cyclo-oxygenase-2 and vascular endothelial growth factor positive.