COW-2020-32

1. b

1. Mixed epithelial and stromal tumor

Grossly, a solid and multicystic white tumor measuring up to 74 mm was centred on the medulla of the kidney with extension into the dilated pelvicalyceal system. There was polypoidal prolapse of tumor into the upper ureter without any obvious adherence of this component to the ureteric wall. This had given the radiological impression of an upper tract urothelial carcinoma. The histology revealed a biphasic tumor composed of cellular ovarian-type stroma and multiple cysts lined by a single layer of bland cuboidal epithelium focally with hobnail morphology. The tumor was well demarcated but not encapsulated. There was no atypia in either the stromal or epithelial component, and mitoses were not apparent. There were no areas of necrosis or hemorrhage apart from a small area of ischemic change in the distal component of the ureteric element.

Immunohistochemistry revealed the stromal component as positive for estrogen receptor (ER), progesterone receptor (PR), smooth muscle actin, desmin, vimentin, and CD10, with accentuation of ER, PR and CD10 around the epithelial-lined cysts. The epithelium was positive with pancytokeratin, Cytokeratin 7, and vimentin. HMB45, Melan-A, Calretinin and Inhibin were negative. MIB1 showed a low proliferative index of less than 1% .

Mixed epithelial and stromal tumor (MEST) is a rare, almost exclusively benign tumor which affects predominantly perimenopausal females. These tumors are often associated with endogenous hormone treatment or obesity. Rare cases in males are often associated with long-term sex steroid exposure. One previously published case report also demonstrated ureteric prolapse; a further case demonstrated renal vein and IVC polypoidal growth. Extremely rare cases have shown sarcomatoid malignant transformation, including carcinosarcoma, but the vast majority follow a benign course. Occasional cases of MEST have been associated with translocation t(1:19).

MEST may be part of a spectrum with adult cystic nephromas (CN), which show a similar histology, but with a lower stroma to epithelium ratio and lower proportion of ovarian-type stroma. The immunohistochemical and molecular profiles of the two appear similar and different from other renal tumors. Both tumors also show similar expression profiles of mRNA with high expression of Insulin-like growth factor 2 and low expression of Carbonic Anhydrase 2 genes.

In recent years, angiomyolipoma with epithelial cysts (AMLEC) has been described. This rare variant of angiomyolioma can be distinguished from MEST by the finding of positive staining of the stromal element with HMB45 or Melan-A. In addition, areas of mature fat or vessels typical of AML may be found focally.

Multilocular cystic renal neoplasm of low malignant potential lacks the cellular or ovarian type stroma seen in MEST and does not show expression of ER and PR.

Tubulocystic carcinoma can be differentiated by a greater degree of pleomorphism within the cells lining the cysts and tubules. The stroma also tends to be fibrotic in nature. In addition there is no staining with ER or PR.

Also in the differential is a Synovial sarcoma but this typically has a much more cellular appearance and more infiltrative growth pattern with high mitotic activity and positive FISH for the SYT-SSX gene fusion.

Jung SJ, Shen SS, TranT, et al. Mixed epithelial and stromal tumor of kidney with malignant transformation: report of two cases and review of literature. Hum Pathol. 2008;39(3):463–468.

Turbiner J, Amin M, Humphrey PA, et al. Cystic nephroma and mixed epithelial and stromal tumor of kidney: a detailed clinicopathologic analysis of 34 cases and proposal for renal epithelial and stromal tumor (REST) as a unifying term. Am J Surg Pathol. 2007;31(4):489–500.

Horikawa M, Shinmoto H, Kuroda K, et al. Mixed epithelial and stromal tumor of the kidney with polypoid component extending into renal pelvis and ureter. Acta Radiologica Short Reports 2012;1:3.

Sountoulides P, Koptsis M, Metaxa L, et al. Mixed epithelial and stromal tumor of the kidney (MEST) simulating an upper tract TCC. Can Urol Assoc J 2012;6(1):e23-26.

Picken MM, Bova D, Pins MR, et al. Mixed Epithelial and Stromal Tumor of the Kidney with Extension into Inferior Vena Cava. Case Report and Discussion of Adult Biphasic Cystic Renal Lesions and the Significance of Vascular Involvement. Case Rep Pathol. 2018: 8234295.

Wang C, Lin Y, Xiang H, et al. Mixed epithelial and stromal tumor of the kidney: report of eight cases and literature review. World Journal of Surgical Oncology 2013, 11:207.

Amy Leeming
Marie O’Donnell

Western General Hospital
Edinburgh, Scotland

Kidney, ureter

MEST; mixed epithelial and stromal tumor; biphasic; renal