A new case of malignant mixed epithelial and stromal tumor of the kidney with rhabdomyosarcomatous transformation.

We report a new case of an epithelial and stromal tumor of the kidney (MESTK) with sarcomatous mesenchymal transformation, rhabdomyosarcoma. The patient was a 62-year-old female complaining of left abdominal pain. A renal mass was discovered and a left radical transperitoneal nephrectomy and left paraaortic lymphadenectomy was performed, in addition to complete excision of a thrombosed renal vein up to its cava connection. Grossly the tumor measured 5 × 4.5 × 4 cm and was located at the lower pole of the kidney, protruding on the renal surface (Figure 1A); it reached sinus fat and macroscopically grew into the renal vein. It was a relatively well-circumscribed, cystic and solid white-tan tumor with a big cyst with clear fluid inside and some smaller and minute peripheral cysts. The mass had a soft consistency, focal necrosis and hemorrhage. Histologically it was a biphasic tumor with benign epithelial cysts and a variably cellular surrounding mesenchyma (Figure 1B). Sometimes it was bland and focally sclerosed, or denser, fascicular and frequently sarcomatous. Cysts were lined by Müllerian (cuboidal, columnar, ciliated) and hobnailed epithelium. Some smaller cysts appeared forming aggregates, with light pink secretion inside; a few larger cysts had a phyllodes-like overgrowth of surrounding stroma (Figure 2A). Cysts appeared surrounded by “cuffs” of bland, dense, spindle cell stroma (sometimes ovarian-like) admixed with occasional desmin and myogeninpositive bizarre multinucleated cells, rhabdomyoblasts (Figures 3 and 4) which became more common and confluent towards the center of the mass, interspersed with bland, edematous, occasional hemangiopericytic-like areas with short-plump spindle cells, isolated calcifications and collagenous and hyalinized foci. Sarcomatous stroma was predominant (75% of the total). In most active areas there were a maximum of 12 mitotic figures/10 high-power field, some atypical. There were no carcinomatous elements or other heterologous, PEComatous, clear-cell aggregates or blastema components after sampling the entire tumor specimen. Lymphovascular sarcomatous invasion was frequent. The renal vein contained a neoplastic thrombus. Sinus fat tissue was focally infiltrated by the sarcomatous component. Nonneoplastic kidney had no relevant lesions. Hilar, periadrenal, paraaortic lymph nodes and left adrenal gland were free of tumor. Immunohistochemical studies showed that epithelia expressed cytokeratin (CK) AE1/3, CK7, EMA and CK5/6. Benign stromal cells were diffusely positive for Vimentin (Vim), CD10, smooth muscle actin (SMA), desmin and CD56. Stromal pericystic cells intensively expressed bcl-2 Analytical and Quantitative Cytopathology and Histopathology ®