PMC8149592_01
Histological and immunohistochemical features of a hibernoma (pale cell variant) in the subepidermal area of the nipple in a bitch. (A) The subepidermal area of the nipple is distended by an expansile, benign tumor (white asterisk), HE stain. (B,C) The tumor is composed of round to polygonal neoplastic brown fat cells arranged into sheets and poorly defined lobules, separated by a fine fibrovascular stroma. The neoplastic cells show abundant vacuolated cytoplasm, and mild anisocytosis and anisokaryosis, HE stain. (D) The neoplastic cells are negative for cytokeratin AE1/AE3, but positive for Vimentin (E) and UCP1 [(F) and higher magnification in the inset]. IHC.
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F1
Positive controls consisted of sections of mouse perirenal adipose tissue (Supplementary Figure 1) and canine sebaceous gland adenocarcinoma (Supplementary Figure 2) known to express UCP1 and p53, respectively. Histological examination revealed a well-defined, partially encapsulated, multinodular and highly cellular neoplastic mass, effacing and expanding the subepidermal area of the nipple (Figure 1A). The neoplastic cells presented variably distinct cellular borders, clear or pale eosinophilic cytoplasm, containing one or multiple optically empty vacuoles, mainly resembling lipocytes (Figure 1B). Anisocytosis and anisokaryosis were mild, and the number of mitotic figures varied from 0 to 2 per high power field (0.237 mm2) (Figure 1C).