Adrenal cortical carcinomas with myxoid differentiation in the domestic ferret (Mustela putorius furo).

A total of 15 adrenocortical carcinomas with myxoid differentiation from 15 ferrets were evaluated in this retrospective study. Six of these ferrets (40%) either were euthanatized or died due to invasive and/or metastatic disease. The myxoid component was a variable part (between 5% and 95%) of the adrenal cortical neoplasm and consisted of sheets and cords of small, polygonal neoplastic cells that formed lumenlike spaces. Such spaces contained a variable amount of alcian blue (pH 2.5)-positive mucinous product (i.e., acidic mucopolysaccharides). Neoplastic cells were negative for the argentaffin reaction, but immunohistochemically they were strongly positive for vimentin and alpha-inhibin and lightly positive for synaptophysin. Proliferating cell nuclear antigen (PCNA)-labeling indices (LI) of adrenal cortical neoplastic cells within the myxoid component of the neoplasm were significantly elevated (P < 0.05) compared with those of typical neoplastic adrenal cortical cells or the adjacent nonneoplastic zona reticularis. Ultrastructurally, cells in the myxoid component exhibited a typical adrenocortical phenotype characterized by cytoplasmic lipid vacuoles, prominent rough and smooth endoplasmic reticulum, and zonula adherens. This lesion was interpreted as an adrenal cortical carcinoma with myxoid differentiation and appeared to be highly malignant based on PCNA LI, rate of invasion into adjacent tissue, and metastasis (6/15). This report is the first description of this histologic variant in the ferret, which morphologically resembled the rare myxoid variant of adrenocortical carcinoma described in humans.