Mixed epithelial and stromal tumor of the kidney

We describe the clinicopathologic features of 12 patients with a distinctiv e tumor of the kidney characterized by a mixture of epithelial and stromal elements that form solid and cystic growth patterns. Similar tumors were re ported previously in the literature under various names, including adult me soblastic nephroma. All but one of the patients were women. The only man ha d a long history of treatment with lupron and diethylstilbesterol. Seven of the women had histories of long-term oral estrogen use of whom six had und ergone total abdominal hysterectomy and bilateral salpingo-oophorectomy sev eral years prior, and the seventh patient had been using oral contraceptive s for many years. Another woman had this operation but did not receive any hormone therapy. Ages ranged from 31 to 71 years (mean, 56 yrs). Six patien ts presented with symptoms, including pain and infections attributable to m ass effect, and in six the tumor was detected incidentally. Grossly, the tu rners were well-circumscribed (mean size, 6 cm; range, 3-12 cm) and consist ed of solid and cystic components, most often in equal proportions but in v ariable distribution. Microscopically, the spindle cell component ranged in appearance from scar-like fibrous tissue to leiomyoma-like interlacing fas cicles; usually there was a mixture of both. More cellular foci reminiscent of ovarian stroma or solitary fibrous tumor were also present. No blastema was present. Epithelial elements (composed of clusters of tubules with var iable lining) were scattered amidst the spindle cells, and focally transfor med into large cysts lined by cells with abundant pink cytoplasm and a hobn ail appearance. immature epithelial elements typical of Wilms' tumor were n ot present. Muscle markers (desmin and smooth muscle actin) were positive d iffusely and strongly in the spindle cells of all tumors, whereas HMB-45 an d CD34 were absent. Estrogen receptors were detected in the nuclei of spind le cells in seven tumors and progesterone receptors in three. The distincti ve clinicopathologic characteristics of these lesions warrant their classif ication as a separate category of kidney tumor. We suggest the descriptive term "mixed epithelial and stromal tumor" for this group until its nature a nd relationship to other kidney lesions are further clarified. Its preponde rance in females with a history of long-term estrogen replacement and the h istory of long-term sex-steroid use in thr only male patient, combined with the frequent content of estrogen and progesterone receptors in the spindle cells, suggest that the hormonal milieu plays a role in the evolution of t hese tumors. The clinical and pathologic parallels with mucinous cystic tum ors of pancreas and liver raise the possibility of a common pathogenetic me chanism that may be linked to the periductal fetal mesenchyme. We think thi s entity is a benign composite neoplasm in which stroma and epithelium are both integral neoplastic components.