Diagnosis, Differential ; Humans ; Kidney ; pathology ; Kidney Neoplasms ; diagnosis ; pathology ; Nephroma, Mesoblastic ; diagnosis ; pathology

The descriptive term "mixed epithelial and stromal tumor of the kidney" was recently proposed for a group of renal tumors characterized histologically by a mixture of stromal and epithelial proliferation. It is a rare benign neoplasm of the kidney which has been reported under various names such as adult type mesoblastic nephroma or others. We report a case of mixed epithelial and stromal tumor in a 47 yr old female patient presenting as a partly cystic and partly solid renal mass. Microscopically, the tumor exhibited spindle cell component in solid portion and epithelial proliferation around microcystic areas. Immunoreactive profiles and ultrastructural examination suggested myofibroblastic nature of the stromal cells. We believe this case exemplifies a unique adult renal tumor displaying both epithelial and stromal neoplastic component and has a few unusual features worthy of attention.
Nephroma, Mesoblastic/pathology ; Neoplasms, Glandular and Epithelial/*pathology ; Middle Aged ; Kidney Neoplasms/*pathology ; Humans ; Female ; Diagnosis, Differential

Adenofibroma ; metabolism ; pathology ; Antigens, CD34 ; metabolism ; Child, Preschool ; Diagnosis, Differential ; Female ; Humans ; Kidney Neoplasms ; metabolism ; pathology ; surgery ; Neoplasms, Germ Cell and Embryonal ; metabolism ; pathology ; surgery ; Nephroma, Mesoblastic ; metabolism ; pathology ; Sarcoma, Clear Cell ; metabolism ; pathology ; Stromal Cells ; metabolism ; pathology ; Vimentin ; metabolism

OBJECTIVETo study the clinicopathologic features, immunophenotype and differential diagnosis of mixed epithelial and stromal tumor of kidney (MEST) and adult cystic nephroma (CN).

METHODSFive cases of MEST and 4 cases of CN were retrospectively analyzed. Immunohistochemical study was carried out and the literature was reviewed.

RESULTSAll of the five patients with MEST were females. Their median age was 45 years. For CN, there were 3 males and 1 female and their median age was 41 years. All patients presented with loin pain and hematuria. On gross examination, MEST was well-circumscribed but non-encapsulated. There was no evidence of haemorrhage or necrosis. Three of the cases were solid in nature. One was composed of a mixture of solid and cystic elements, while the remaining case showed a multicystic cut surface bridged by thick fibrous septa. On the other hand, CN were well-circumscribed and encapsulated. They were multiloculated cystic in nature. The cystic spaces were separated by thin septa and there was no significant solid or necrotic component. Histologically, MEST consisted of proliferation of cystically dilated glands admixed with spindly stromal cells with various cellularity and growth patterns. Both the glandular and stromal elements were well-differentiated with no cytologic atypia identified. The glandular structures in 2 of the cases were partially lined by endometrial or tubal epithelium. In contrast, the thin-walled cystic spaces in CN were lined by a single layer of epithelium.Immunohistochemical study showed that the epithelial cells were positive for pan-cytokeratin and epithelial membrane antigen. The spindle cells in MEST expressed vimentin (5/5), smooth muscle actin (3/5), desmin (4/5), CD10 (5/5), estrogen receptor (4/5) and progesterone receptor (4/5). They were negative for HMB45, CD34, CD117 and S-100 protein. On the other hand, the spindle cells in CN were variably positive for vimentin (4/4), smooth muscle actin (4/4), desmin (1/4), estrogen receptor (3/4) and progesterone receptor (1/4). They were negative for CD10, HMB45, CD34, CD117 and S-100 protein.

CONCLUSIONSBoth MEST and CN are uncommon renal neoplasm. Most of them run a benign clinical course. The stromal cells in MEST show smooth muscle or myofibroblastic differentiation. Areas demonstrating Müllerian features also existed in some cases. MEST and CN share overlapping histological and immunohistochemical features, and may represent spectrum of the same group of lesions.

Actins ; metabolism ; Adult ; Carcinoma, Renal Cell ; pathology ; Desmin ; metabolism ; Diagnosis, Differential ; Epithelial Cells ; metabolism ; pathology ; Female ; Follow-Up Studies ; Humans ; Kidney Neoplasms ; metabolism ; pathology ; Male ; Middle Aged ; Neoplasms, Complex and Mixed ; metabolism ; pathology ; Neoplasms, Cystic, Mucinous, and Serous ; metabolism ; pathology ; Nephroma, Mesoblastic ; pathology ; Receptors, Estrogen ; metabolism ; Retrospective Studies ; Stromal Cells ; metabolism ; pathology ; Vimentin ; metabolism