Malignant mixed epithelial and stromal tumor of the kidney

Abstract

Sir, We report a case of a mixed epithelial and stromal tumor of the kidney with malignant transformation of its mesenchymal component. A 46-year-old woman was operated on for a computed tomography-proven solidified cyst in the upper pole of the left kidney. No tumorous metastatic dissemination was found during further clinical examination.The kidney contained a cystic tumor 7 cm in diameter bulging into the perirenal fat. The gray-brown wall of the cyst was 0.2-to 0.3-cm thick, the inner surface was smooth, covered by light and dark brown, hemorrhagic material. A flat, red-brown prominence measuring 4×3×1.5 cm, multilocular on a cut surface, protruded into the intracystic space. The margins of the tumor were sharply demarcated from the renal parenchyma but were indistinct on the side of perirenal fat. The hemorrhagic contents of the cyst, submitted separately in a total volume of about 200 ml, were characteristic of blood clots, seemingly free of tumorous material. The renal parenchyma outside the tumor area, renal pelvis and ureter were unremarkable.The tumor showed a histological structure of a benign multilocular cyst containing cysts and septa, which comprised occasional small tubular structures. Septa were formed by fibrous stroma with uneven cellularity focally displaying ovarian stroma-like features (Fig. 1) and immunohistochemically showing positivity of vimentin, smooth muscle actin, muscle actin and desmin. Ultrastructurally, the bland-looking cells surrounded by external lamina and connected by primitive attachment sites were set in the background of collagenous matrix. They contained numerous organelles, including copious cisternae of the rough and smooth endoplasmic reticulum, intermediate filaments and Golgi complex. Numerous patches of microfilaments were focally present in the cytoplasm of the benign stromal cells. The tubules and cysts were lined with a single layer of epithelial cells, mostly showing a hobnail appearance, oxyphilic, periodic acid-Schiff base (PAS)-negative cytoplasm and large, irregular nuclei. PAS-positive material was present in some lumina. Immunohistochemically, the cells were cytokeratin and epithelial membrane antigen (EMA) positive. No heterologous tissue, renal blastema cells or poorly differentiated epithelial structures were found.

Mixed epithelial and stromal tumour of the kidney: imaging features

“…Malignant transformation has also been reported in the solid, stromal component of a MEST in a 84-year-old woman [14]. In all malignant cases [12][13][14] the epithelial lining of the multicystic component had no evidence of malignancy.…”

“…However, malignant cases have been reported [12][13][14]. Svec et al [12] described a malignant MEST in a 46-yearold woman. The multicystic component was benign, but there was malignant transformation of the solid, mesenchymal component.…”

“…The role of percutaneous biopsy in such lesions is limited [28]. Biopsy could be considered; the retrieval of ovarian stroma could potentially be used to suggest the diagnosis, but ovarian stroma could be found in cystic nephroma [29] and rarely in the malignant form of MEST [12][13][14].…”

“…A strong association with oestrogen exposure was proposed. Of the 90 patients reported who had MEST [1][2][3][5][6][7][8][9][10][11][12][13][14][15][16][17][18], almost all have been women [2,4]. Many of these patients were perimenopausal with a history of long-term oestrogen replacement at the time of diagnosis [2].…”

“…Although there are case reports and series in the pathology literature [1][2][3]6,7,[9][10][11][12][13][14]16,17] there are few published reports describing the imaging findings of MEST [5,8,19]. To the best of our knowledge, the largest radiological study described the imaging features in three patients [5].…”