Adrenocortical tumors with myxoid features: a distinct morphologic and phenotypical variant exhibiting malignant behavior.

Myxoid changes have been rarely reported both in adrenocortical adenomas and carcinomas. The recent observation by our group of an adrenal myxoid tumor with morphologically borderline features, but aggressive clinical behavior prompted us to review a series of 196 adrenocortical lesions, comprising 122 carcinomas and 74 adenomas, to define the morphologic, phenotypical and clinical characteristics of adrenocortical tumors with myxoid features. Fourteen cases, including 12 carcinomas and 2 borderline tumors, formed the basis of this report, and were characterized by a variably abundant myxoid component (from 5% to 90% of tumor) and 2 distinct cellular growth patterns: the first (10 cases), mostly associated with a predominant myxoid stromal component, was made of small cells with mild atypia arranged in cords and microcysts; the second (4 cases) was characterized by focal myxoid changes in tumors otherwise similar to conventional adrenocortical carcinoma, with large atypical cells having an eosinophilic cytoplasm and a diffuse or nodular architecture. The above mentioned patterns were absent in all adenomas reviewed. A peculiar reactivity to neurofilaments was seen, mostly associated to the presence of predominant rather that focal myxoid stromal changes, and in 40% of conventional adrenocortical carcinomas, thus representing an undescribed potential pitfall in the differential diagnosis of adrenal lesions. Myxoid adrenocortical tumors probably represent a rare but histologically and phenotipically distinct entity and, although rare cases of benign lesions are on record, they seem to be generally associated to morphologic and clinical features of malignancy.