Mixed Epithelial and Stromal Tumor of the Kidney (MESTK)
Michal Michal, M.D. Medical Faculty Hospital Pilsen, Czech Republic
A 48 year-old woman was seen for flank pain and a right abdominal mass. A right kidney tmnor was excised.
The resected kidney measured 16x14x12 cm. The tumor was localized in the central part of the kidney. It
was 10 cm in diameter, round, well circumscribed with a thin fibrous capsule. There were no signs of
infiltrative growth into the surrounding renal parenchyma. The tumor was situated within the renal
parenchyma and compressed the adjacent calyceal system. Grossly the tumor had a solid appearance without
cyst formation, with a white cut surface, and soft to elastic consistency without hemorrhage or necrosis.
The tumor had distinct adenomatous and mesenchymal components. The adenomatous component consisted of
variously sized ducts, which ranged from very minute, ductuli with a thick basal membrane to larger ducts
with well formed lumina. The largest ducts contained cells with "hobnail" appearance. The cytoplasm of the
cells in the ducts stained deeply red with H&E stain. The duct contained PAS and Alcian Blue positive and
mucicarmine negative secretion and the cytoplasm of the cells of the adenomatous component was often deeply
eosinophilic. The adenomatous component was surrounded by a spindled mesenchymal stroma. The spindle cells
closely resembled ovarian stroma. Sparse small lymphocytes were also present in the stroma. This
ovarian-like stroma suuounded clusters of small neoplastic ductules or grew among the larger ducts. The
stroma was always centered on the adenomatous component and never formed compact sheets devoid of
adenomatous elements. In spite of the similarity of the mesenchymal component to the ovarian stroma,
follicle-like structures, specialized gonadal stromal structures or luteinization characteristic of the
ovary was absent. No immature embryonal renal tissue, papillary epithelial differentiation, transitional
urothelial epithelimn or stromal heterologous cellular structures were present in the tumor. No mitoses,
atypia, hemorrhage, necrosis or foci of extramedullary hematopoiesis were observed. A pararenal lymph node,
which was excised together with the right kidney, had a normal structure and was negative for tumor.
Immunohistochemically, the epithelial elements reacted with antibodies to cytokeratins and were negative
with antibodies to synaptophysin, serotonin and chromogranin. The eosinophilic cells in the ducts stained
strongly with antibody to mitochondrial antigen 113-1. Antibodies to EMA and CEA were positive only in the
secretory elements and the superficial glycocalyx of the ducts. The cytoplasm of the neoplastic cells was
negative. The spindle stromal cells were positive with antibodies to muscle actin, smooth muscle actin,
CD34 and desmin (clone D33). Antibody to MIB1 reacted only in less then 1% of the epithelial and stromal
cells revealing thus a very low level of the cell proliferation in the tumor.
The tumor is composed of adenomatous and mesenchymal components. The adenomatous component shows variously sized ductules and ducts with flattened to euboidal cells with a "hobnail" appearance. There is a spindled mesenchymal component.
The tumor is composed of numerous small ductules and a spindled mesenchymal stroma.
The tumor is composed of numerous small ductules and a spindled mesenchymal stromal component.
The tumor contains many small ductules or tubules and the spindled mesenchymal component.
Immuno- cytochemistry for cytokeratin (AE1/AE3). There is intense staining of the cytoplasm of the cells lining the ductules/tubular structures of this tumor.
Diagnosis: Mixed epithelial and stromal tumor of the kidney (MESTK)
MESTK was first desclibed by Michal and Syrucek in 199814 as a renal counterpart of pancreatic and
biliary cystadenomatous neoplasms containing ovarian-like stroma.6,8 Two years later, in the April issue
of Pathology Research and Practice, Michal widened the concept of MESTK, unifying several hitherto variously
designated neoplasms into one distinct entity. These renal tumors were previously designated as adult type
mesoblastic nephroma,19 cystic hamartoma of the pelvis,13,16 adult type of cystic nephroma,9,12
multilocular renal cysts5,7,10 and solid and cystic biphasic tumor of the kidney.1,17 The designation
of benign mixed epithelial and stromal tumor of the kidney (MESTK) was proposed as a unifying term for all
Histologically, all these tumors resemble each other far more than they differ from one another. The main
differences among these tumors are in the relative amount and configuration of their epithelial component,
cellularity and the tumor localization. It seems that when the epithelial component of these tumors is
cystically dilated, they were called cystic nephromas (in adults);9 when the epithelial component was
partly cystic and partly solid, they were called solid and cystic biphasic tumors of the kidney1,17 or
mesoblastic nephromas in adults;19 and when the tumors were located predominantly in the pelvis they were
called cystic hamartomas of the pelvis.13,16
Their common histologic and clinical features include: 1) They nearly exclusively occur in middle aged to
older women, 2) the stroma has the morphology and immunohistochemical properties of ovarian stroma; and 3)
there is always a variably cystic epithelial component with eosinophilic cytoplasm and often hobnail
appearance (similar to collecting ducts).
In the July issue of the American Journal of Surgical Pathology the same year (2000), Adsay et al presented
a practically identical concept for these lesions and expanded the list of tumors previously published under
different names that could fit into the MESTK concept. They further proved that these tumors often express
estrogen/progesterone receptors. Interestingly, the only male patient in their series of 12 cases had a
7-year history of diethylstilbestrol therapy followed by 4 years of lupron for prostatic adenocarcinoma.1
Beiko et al published a case of MESTK of possible Mullerian origin.4 Svec et al reported a synovial
sarcoma arising in MESTK.18 In addition to this reported case, we have seen two cases of synovial
sarcomas of the kidney arising in MESTK. It thus seems that a considerable part of synovial sarcomas
arising in the kidney may have origin in MESTK.3,11
Adsay V, Eble JN, Srigley JR, Jones EJ, Grignon DJ. Mixed epithelial and stromal tumor of the kidney.
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