Myxoid renal tumor with myoepithelial differentiation mimicking a salivary gland pleomorphic adenoma: description of a case

We herein report an unusual case of a low-grade myxoid renal epithelial neoplasm, with peculiar and previously unreported morphologic and immunohistochemical features. The lesion was characterized by noninfiltrative borders, myxoid stroma and elongated tubular and cordlike epithelial structures. These were lined by 2 different epithelial cell types, flat and elongated basal cells and cuboidal to spindle shaped eosinophilic luminal cells, with low-grade nuclear features and a few small nucleoli. The lesion morphologically resembled a pleomorphic adenoma of the salivary gland. The immunohistochemical profile interestingly confirmed the myoepithelial differentiation of the basal epithelial layer, as demonstrated by the coexpression of several myoepithelial markers such as p63, caldesmon, calponin, smooth muscle actin, and S-100, together with epithelial markers such as low and high-molecular weight cytokeratins. The tumor proved benign at follow-up. A definitive classification and histogenetic interpretation of this previously unreported tumor type awaits description of further cases showing similar features which, perhaps, as it may happen, went so far unnoticed.