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Mixed Epithelial and Stromal Tumor of the Kidney: a Case Report

Zekie Kasimova, Hristo Popov, Mariya Tsaneva


Introduction: Mixed epithelial and stromal tumor (MEST) of the renal pelvis, also known in the past as cystic hamartoma is a rare benign tumor, recently recognized as a distinct clinical and pathological entity. This complex neoplasm is composed of a mixture of stromal and epithelial elements. Women are more often involved (ratio of women to men 6:1), especially perimenopausal women. It was originally described in 1973 by Block as a congenital mesoblastic nephroma. The term MEST was credited to Michal and Syrucek in 1998.

Methods and Materials: A 54-year-old woman underwent laparotomy because of pheochromocytoma. In addition, another tumor was found in the left kidney - a partly cystic and partly solid mass in the renal pelvis, so left-sided  nephrectomy was carried out.

Results: Macroscopically, the lesion in the renal pelvis had an oval form, measuring 15/8 cm, well circumscribed from the surrounding parenchyma, and with fatty tissue at the periphery; the cut surface revealed multiple cysts of varying size, showing papillary projections on the inner side. On histological examination, a well-delineated tumor was seen, composed of cysts of varying size lined by columnar and cuboidal epithelium. Surrounding stroma showed a mixture of an ovarian type of stroma and eosinophilic loci resembling white bodies and a lot of calcifications.

Conclusion: Only about 200 cases of MEST have been described in the literature. Mixed epithelial and stromal tumor of the kidney usually presents in perimenopausal women as a partially cystic mass, and its growth may be influenced by hormones. In the literature, there is no other description of coexisting  MEST and pheochromocytoma.


mixed epithelial and stromal tumor, MEST, renal cyst, pheochromocytoma


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