Smooth muscle and adenoma-like renal tumor: a previously unreported variant of mixed epithelial stromal tumor or a distinctive renal neoplasm?

We describe 6 cases of a biphasic renal neoplasm, which we designate smooth muscle and adenoma-like renal tumor, which do not cleanly fit any category as currently defined. There were 4 females and 2 males (age, 27-70 years); neither male had a history of hormone exposure. All 5 neoplasms with available history were discovered incidentally on imaging studies with sizes ranging from 4 to 20 cm. The stroma was composed of smooth muscle fascicles alternating with looser, edematous areas; none of the cases contained ovarian-like stroma. The complex but cytologically benign epithelial component consisted of tubulopapillary nodules, branching tubules, clefts, and large cysts. The stroma of all of the cases labeled diffusely for desmin. Estrogen receptor labeling was absent in 4 cases with only minimal (<10%) weak labeling in the remaining 2. The epithelial component of each case labeled diffusely for cytokeratin 7 and was patchy for α-methyl-CoA racemase (P504S). Carbonic anhydrase IX, HMB45, WT-1, and inhibin were negative. None of the 5 cases tested demonstrated trisomies of chromosome 7 or 17 by fluorescence in situ hybridization. Two patients with significant follow-up are disease free at 18.5 and 2.5 years. Smooth muscle and adenoma-like renal tumor could potentially represent a variant of mixed epithelial stromal tumor, which would expand its reported spectrum. However, the absence of clinical history of hormone exposure, predominance of smooth muscle with lack of ovarian-like stroma, prominence of epithelial nodules, and typical absence of estrogen receptor labeling suggest that it may represent a distinct entity.