Incidental Stromal-Predominant Mixed Epithelial-Stromal Tumors of the Kidney: A Mimic of Intraparenchymal Renal Leiomyoma

Mixed Epithelial and Stromal Tumor of the Kidney: A Clinicopathologic Study of 53 Cases

Mixed epithelial and stromal tumor of the kidney is an uncommon complex neoplasm, and previous studies have included only a modest number of cases and have left gaps in our understanding of its morphology. We analyzed 53 tumors (46 F, median age: 49 y), collecting data on gross, histologic, and immunohistochemical features. The most common gross appearance was solid and cystic (47%). Hypocellular fibrous and cellular spindle cell stroma were the most common stromal types, followed by smooth muscle differentiation, edematous stroma, and adipose tissue. Hypocellular fibrous stroma and adipose tissue were more common in larger tumors (P=0.003 and 0.04, respectively) and cellular spindle cell stroma in smaller tumors (P=0.0009). Combinations of diverse stromal elements were common: roughly 50% of tumors contained >4 types of stroma. With regard to epithelium, tiny crowded and branching glands were present in 60% of tumors. Round glands lined by tall cuboidal epithelium, reminiscent of thyroid follicles, spatulate papillae reminiscent of phyllodes tumor, glands reminiscent of nephrogenic adenoma, and complex papillae were also frequently found. Combinations of diverse epithelial elements were common: 64% of tumors contained >4 types of epithelium. All of the tumors except 1 were positive for smooth muscle actin in the stroma. Desmin and caldesmon expression were more variable. Stains for progesterone and estrogen receptors showed positivity in the stromal component in 85% and 73% of tumors, respectively. CD10 and CD34 immunolabeling were restricted to pericystic spindle cells. No tumor expressed inhibin. In summary, this study demonstrates a strong tendency for mixed epithelial and stromal tumors to contain multiple types of stroma and epithelium and comprehensively analyzes the immunohistochemical profile.

Expanding the Morphologic Spectrum of Adult Biphasic Renal Tumors—Mixed Epithelial and Stromal Tumor of the Kidney With Focal Papillary Renal Cell Carcinoma

Mixed epithelial and stromal tumor (MEST) is a distinctive adult biphasic neoplasm of the kidney characterized by the presence of solid and cystic areas composed of spindled stroma and epithelium lining tubules and cystic spaces respectively. Most MESTs are benign although sarcomatous transformation has rarely been reported. It has not been clearly established whether the epithelial component represents entrapped tubules or constitutes a true neoplastic component. We report an unusual case of a biphasic tumor of the kidney with a benign stroma and a focal component of papillary carcinoma arising in one of the cysts and discuss its pathogenesis.

Cellular metanephric stromal tumor in a postmenopausal woman: a case report with review of the literature

Metanephric stromal tumor (MST) of the kidney is a rare pediatric neoplasm which has rarely been reported in adults. The authors present a case of MST, cellular type, an unreported variant, in a 56-year-old postmenopausal woman. The 9.0-cm tumor was solid, unencapsulated, and well circumscribed, with a firm homogeneous cut surface. The tumor was purely stromal with dense spindle-cell proliferations displaying prominent schwannoma-like architecture, intratumoral angiodysplasia, and entrapped native renal tubules with "onion-skin" tumor collarettes. The tumor stroma expressed CD34, estrogen, and progesterone and did not express desmin, smooth muscle actin, S-100, or TLE-1. Considering the characteristic morphology and immunophenotype, a diagnosis of "metanephric stromal tumor, cellular type," was made. This is an exceptionally rare disease manifestation in an adult patient and the first description of MST with such high stromal cellularity, making this case unique in both clinical and pathological presentation.

Fat-predominant mixed epithelial stromal tumor (MEST): report of a unique case mimicking angiomyolipoma

A unique case of a mixed epithelial stromal tumor (MEST) that was predominantly composed of adipose tissue is reported here. Radiographically and grossly, the lesion was thought to be an angiomyolipoma, based upon its fatty appearance. Microscopically, the lesion was predominantly composed of mature adipose tissue but also contained clusters of bland tubules surrounded by smooth muscle bundles and collagen. By immunohistochemistry, the stroma labeled diffusely for estrogen and progesterone receptors, while the muscle bundles labeled for desmin. Melanocytic markers HMB45 and Melan A, typically positive in angiomyolipoma, were nonreactive. This case expands the morphologic spectrum of MEST to include mimics of angiomyolipoma.

Large mixed epithelial and stromal tumor of the kidney masquerading as metastatic renal cell carcinoma

We report the case of a 39-year-old woman with a large right renal mass 20 cm in size with heterogeneous solid and cystic components as well as concurrent liver lesions suspicious for metastatic renal cell carcinoma. Surgical extirpation of the renal mass and liver lesions was performed laparoscopically with the pathological analysis revealing a rare renal neoplasm--mixed epithelial and stromal tumor of the kidney--and adenomas of the liver.

Mixed epithelial and stromal tumour (MEST) of the kidney: report of 14 cases with male and PEComatous variants and proposed histopathogenesis

AIMS

This article adds new cases and variants of MEST with discussion of the histopathogenesis.

METHODS AND RESULTS

Fourteen MEST were originally diagnosed as cystic nephroma which represents an incidence of 1.6% of renal neoplasms in adults. In females, the stromal component showed areas of müllerian differentiation with positive immunoreactivity for oestrogen (ER) and progesterone receptors (PR) and CD10. Immunoreactivity for HMB45 was identified in a single case having a leiomyomatous appearance. The epithelial component displayed features of müllerian epithelium and reactive renal tubular cells. In two male cases, MEST consisted of fibrous and smooth muscle stroma and cysts lined only by reactive renal tubular cells. Immunoreactivity for ER and PR was focal and weak.

CONCLUSIONS

MEST represents a tumour developing from müllerian-like stromal cells in the kidney. The neoplastic stroma encroaches on the renal tubules and has the potential to stimulate the growth of the renal tubules by contact, with development into cysts. Furthermore, the müllerian stroma likely induces the renal tubules to differentiate into müllerian-like epithelium. Melanocytic differentiation of the stroma may occur which represents the PEComatous variant. MESTs in males were histopathologically slightly different from those in females due to the different hormonal milieu.

Synchronous sertoli cell and serous cystadenoma tumors of the ovaries with mixed epithelial and stromal tumor of the kidney: a case report

We present a rare case of a 68-year-old postmenopausal woman with a mobile, hard, and painless pelvic abdominal mass that was palpated to the umbilical scar. Ultrasonography demonstrated a solid mass in the upper pole of the right kidney and a predominantly solid pelvic abdominal mass. Serum testosterone was 413 ng/dL. The patient underwent laparotomy on the renal tumor, which was thought to have a probable ovarian metastasis. Bilateral ovariectomy and right nephrectomy were performed. Immunohistochemical and histopathologic assessment identified a right ovarian Sertoli cell tumor, a left ovarian serous cystadenoma, and a mixed epithelial-stromal tumor in the kidney with positive hormonal receptor. Because our patient had an ovarian neoplasm producing steroids and a kidney tumor expressing hormonal receptors, the hypothesis of possible endocrine dependence in the pathogenesis of mixed epithelial stromal tumor is reinforced.

Angiomyolipoma With Epithelial Cysts (AMLEC)

Renal angiomyolipoma (AML) is typically a solid lesion, composed of varying amounts of adipose, vascular, and muscular tissue, lacking an epithelial component. Although it is known that entrapped renal tubules may be observed in AML, presentation as a cystic mass has not been previously reported. We report the clinicopathologic and immunohistochemical features of four cystic renal AML. The lesions were found in 2 male and 2 female patients, ranging in age from 37 to 76 years, none with a history of hormonal therapy. One of the four patients had known tuberous sclerosis, and this patient and 1 other presented with bilateral cystic renal lesions. Grossly, the lesions measured between 1.3 and 4.5 cm in greatest dimension. Histologically, the lesions were each composed of three components: 1) epithelial cysts lined by cuboidal to hobnail cells; 2) a compact subepithelial "cambium-like" layer of cellular, müllerian-like AML stroma with prominent admixed chronic inflammation; and 3) muscle-predominant AML with associated dysmorphic blood vessels exterior to the cellular subepithelial stroma. Immunohistochemically, the stromal components of all four lesions labeled with HMB-45 and Melan-A, most intensely in the cellular subepithelial stroma, whereas smooth muscle actin and desmin demonstrated the opposite pattern, with greatest intensity in the muscle-predominant AML areas. Immunoreactivity for estrogen and progesterone receptors (ER, PR) and CD10 was present in all cases, with strongest and most diffuse staining in the subepithelial AML cells. The cyst lining cells were positive for pancytokeratin and soy bean agglutinin (the latter characteristic of distal nephron epithelium) but did not label for ER, PR, or melanocytic markers. Although these distinctive lesions may be confused with mixed epithelial-stromal tumor, their lack of female predominance or association with hormone therapy, their distinctive dysplastic blood vessels and disorganized exterior muscular layer, along with their immunohistochemical profile, support their classification as AML with epithelial cysts. Whereas the cysts appear to arise primarily from entrapped collecting ducts, the peculiar subepithelial condensation of AML stromal cells, with morphologic and immunohistochemical features suggesting differentiation toward endometrial stroma, may represent epithelial-induced müllerian differentiation not previously reported in AML.

Cystic angiomyolipoma of the kidney: a clinicopathologic description of 11 cases

This report deals with 11 examples of renal angiomyolipomas (AML) which appear to include an epithelial element as a part of the neoplasm in the form of gross or microscopic cysts-usually both. There were seven females and four males between the ages of 20 and 70 years with mean age of 45 years. Three of these were known to be symptomatic: intermittent flank pain and gross hematuria for 2 months; recurrent hematuria both before and after flank trauma and a third patient with acute abdomen due to a ruptured tumor blood vessel. Cysts were described in three of the six cases where radiographic data were available. Seven tumors were in the right kidney and four in the left. In gross descriptions, cysts were mentioned in seven and they ranged from 6.0 to 2.0 cm with a median and mean maximal diameter of 5.0 and 4.0 cm, respectively. Microscopically, virtually all of the tumors included multiple smaller cysts and these were lined by flat, cuboidal or columnar epithelium and occasionally hobnail epithelium. There was usually a subepithelial collar of poorly differentiated cells, but the solid element of all tumors was myomatous angiomyolipoma; only one case had any adipose tissue. A dominant histological feature was the prominent lymphatic channels-identical to those of lymphangiomyomas and myomatous or triphasic AMLs. They are much more conspicuous in these cystic cases. Immunohistochemically, all tumors tested were reactive with actin, desmin and HMB-45, with the latter being more intensely positive in the subepithelial collars. Estrogen and progesterone receptors were usually positive, also. The behavior of these lesions appears to be no different from that of other AMLs.