|LETTER TO EDITOR
|Year : 2010 | Volume
| Issue : 3 | Page : 345-346
Mixed epithelial and stromal tumor of the kidney
BN Nandeesh1, T Rajalakshmi1, Hasit Mehta2
1 Department of Pathology, St.John's Medical College, Bangalore-34, India
2 Department of Urology, Narayana Hrudayalaya, Bangalore, India
|Date of Web Publication||28-Jun-2010|
B N Nandeesh
Department of Pathology, St.John's Medical College, Bangalore-34
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Nandeesh B N, Rajalakshmi T, Mehta H. Mixed epithelial and stromal tumor of the kidney. Indian J Cancer 2010;47:345-6
A wide variety of benign epithelial and stromal tumors occur in the kidney. Some of these tumors are unusual and are often clinically/radiologically mistaken for malignant lesions. We describe here one of those rare, recently recognized tumors of kidney.
A 49-year-old lady presented to the surgical department with recurrent colicky left loin pain associated with hematuria since 6 months. The general physical and systemic examinations were not contributory. Urine analysis revealed microscopic hematuria (3-4 red blood cells per high power field). Abdominal ultrasound showed a cystic to solid heterogenic lesion situated in the mid-portion of the left kidney. Contrast computed tomography of the abdomen suggested a Bosniak type 3 cystic renal mass and a possibility of malignancy. A clinical diagnosis of multicystic renal cell carcinoma was made and a left nephrectomy was performed.
Grossly, the kidney appeared asymmetrically enlarged. Cut section revealed a nodular, encapsulated tumor measuring 6 Χ 6 cm. The tumor was partly solid and cystic. The cyst was multiloculated and filled with clear fluid. The solid area was soft to firm and grey brown. Microscopically, the tumor was biphasic with an epithelial and a stromal component [Figure 1]. The epithelial component was composed of tubules and cystic spaces lined by bland-looking cuboidal to columnar epithelium [Figure 2]. The stroma was compact, cellular, and composed of spindle to oval cells with plump nuclei and moderate amounts of eosinophilic cytoplasm [Figure 2]. A final histopathologic diagnosis of "mixed epithelial and stromal tumor of the kidney (MEST)" was offered.
The name "MEST" was first introduced by Michal and Syrucek  in 1998. It is a rare biphasic tumor with approximately 50 cases being described in the literature and to the best of our knowledge only 2 cases have been described in Indian literature.  The tumor is preponderant in adult women with a mean age of 46 years.  The possible cell of origin is considered to be the primary mesenchymal metanephric blastema that has the capacity for mesenchymal and epithelial differentiation.  An alternative theory is that a deranged hormonal milieu (perimenopausal changes or therapeutic hormones with unopposed estrogen) induces proliferation of periductal fetal mesenchyme, which drives the growth of the epithelial component and development into cysts. 
About 75% of patients present with symptoms, such as pain or hematuria, or signs of infection. The remaining 25% of lesions are identified by imaging. The mean diameter in the largest series was 6 cm, with a size range of 3 to 12 cm.  The differential diagnosis is limited as this tumor has unique features with biphasic components. However, if one of the components predominates (especially the stromal one) the differentials can become broad and include medullary fibroma, metanephric stromal tumor, solitary fibrous tumor, stroma-rich angiomyolipoma, and leiomyoma. However, cystic nephroma is a rare cystic tumor, which closely resembles MEST and shares overlapping features. Antic and co-workers  have suggested that these 2 lesions may represent the spectrum of a single entity, rather than 2 separate lesions, and that the tubules may be entrapped rather than comprise an intrinsic component of the tumor. However, further studies, including molecular studies, are needed to support this hypothesis.
Immunohistochemistry is often not necessary because of morphologically distinct features. Although benign, cases of malignant MEST are reported.  The overall prognosis for this tumor is favorable. No recurrent disease has been detected in the present case during 2 years of follow-up. The present case contributes in understanding the pathology of a rare, mostly benign renal neoplasm (MEST) with distinct histopathologic features. This has to be distinguished from other neoplasms, particularly malignant ones, which they simulate clinically and radiologically.
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[Figure 1], [Figure 2]