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Year : 2022  |  Volume : 65  |  Issue : 4  |  Page : 963-965
Catechism (Quiz 17)

1 Department of Surgical Pathology, Bone and Soft Tissue, Disease Management Group (DMG), Tata Memorial Hospital (TMH), Homi Bhabha National Institute (HBNI) University, Parel, Mumbai, Maharashtra, India
2 Department of Radiodiagnosis, Bone and Soft Tissue, Disease Management Group (DMG), Tata Memorial Hospital (TMH), Homi Bhabha National Institute (HBNI) University, Parel, Mumbai, Maharashtra, India

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Date of Submission04-Apr-2022
Date of Acceptance05-Apr-2022
Date of Web Publication21-Oct-2022

How to cite this article:
Rekhi B, Panjawani P, Janu A. Catechism (Quiz 17). Indian J Pathol Microbiol 2022;65:963-5

How to cite this URL:
Rekhi B, Panjawani P, Janu A. Catechism (Quiz 17). Indian J Pathol Microbiol [serial online] 2022 [cited 2022 Nov 30];65:963-5. Available from:

   Clinical History and Imaging Results Top

A 19 year-old male presented with a soft tissue lesion in his left forearm. He underwent a radiological evaluation and fine needle aspiration cytology (FNAC), followed by a biopsy and a wide excision.

The ultrasonogram (USG) revealed a well-defined, lobulated hypoechoic lesion with a few hyperechoic areas and peripheral cystic areas and septations within the lesion, seen in the subcutaneous plane, toward the anteromedial aspect of the forearm below the elbow joint. It measured 3.8 cm × 3.1 cm and showed a significant internal vascularity.
Figure 1:

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Figure 2:

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Magnetic resonance imaging (MRI) revealed a multi-lobulated heterogeneous mass with perilesional edema, along the anterolateral aspect of the left elbow joint. The radiological impression was that of a soft tissue sarcoma, likely a synovial sarcoma [Figure 1]a. An FNAC performed elsewhere was reported as a spindle cell tumor.
Figure 1: Hematoxylin and eosin stained sections of the renal lesion showing solid and cystic components (A), composed of biphasic epithelial and mesenchymal components (B and C) with ovarian-like stroma (D)

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Q1. What is the diagnosis?

Q2: Which immunohistochemical stains are likely to be positive in this tumor?

Q3: What is the most frequent underlying genetic abnormality characterizing this tumor?

   Answers of Catechism (Quiz 16) Top

  1. Diagnosis: mixed epithelial and stromal tumor of the kidneys
  2. Differential diagnosis: adult cystic nephroma, multi-locular cystic renal cell neoplasm of low malignant potential, angiomyolipoma with epithelial cysts, renomedullary interstitial cell tumor, and mesoblastic nephroma

Microscopic description: The lesion shows solid and cystic areas [Figure 1]a and is biphasic with epithelial and mesenchymal components [Figure 1]b and [Figure 1]c. The epithelial lining ranges from flat cells, cuboidal cells, to hob-nail cells. The cells are small, benign-looking, show a round to oval nucleus with scant cytoplasm. The mesenchymal component shows spindle cells and resembles ovarian stroma [Figure 1]d. No mitoses, hemorrhage, or necrosis were identified. On immunohistochemistry (IHC), the epithelial lining was positive for Ae1/Ae3, CK7, and PAX8 and the mesenchymal component was positive for ER and negative for HMB45 [Figure 2].
Figure 2: Immunohistochemical staining showing lesional epithelial cells staining positive for CK7 (A) and AE1/AE3 (B) and negative for HMB45 (C). The stromal cells stain positive for ER (D)

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   Discussion Top

Mixed epithelial and stromal tumor (MEST) of the kidneys was first described by Michal and Syrucek in 1998. These lesions are a part of MEST family tumors, with adult cystic nephroma at the opposite end of the spectrum.[1]

MEST are rare and constitute 0.20 to 0.28% of renal neoplasms. These tumors usually affect middle-aged/peri-menopausal women between 36 and 80 years of age (mean age: 46–years, female: male = 6:1)

These tumors are usually benign without recurrence or metastasis, rare malignant transformation has been reported in a few cases. Clinical features include palpable abdominal mass, hematuria, flank pain, and urinary tract infection. In ~25%, these lesions are asymptomatic and incidental findings. Grossly, the tumor can show a wide range of sizes, is well-circumscribed with solid and cystic components.

Microscopically, the tumor shows a biphasic growth pattern with epithelial and stromal (mesenchymal) components. The epithelial component consists of cysts lined by flat, cuboidal, columnar, hob-nail, urothelial-like, clear cells, or ciliated cells. The cells show minimal cytologic atypia. Stroma can be pauci-cellular to hyper-cellular, and shows spindle cells. Areas may show smooth muscle differentiation, fibroblastic, or myofibroblastic differentiation, or ovarian-type stroma with luteinization.[2]

On immunohistochemistry (IHC), the epithelial cells were positive for cytokeratins, PAX8, PAX2, and GATA3 and the mesenchymal component was positive for ER, PR, CD10, inhibin, FOXL2, SMA, Desmin, and Caldesmon, and negative for HMB45 and Cd34.

Adult cystic nephroma is a part of the MEST family and shows overlapping features. It can be differentiated from MEST by its lack of solid components. The multi-locular cystic renal neoplasm of low malignant potential does not have cellular stroma. The cysts are lined by large clear cells with abundant cytoplasm. Angiomyolipoma is a PEComa (perivascular epithelioid cell tumor) and is positive for melanocytic markers such as HMB45 and Melan A. Renomedullary interstitial tumors are rare incidental tumors, usually of small size, and show entrapped renal tubules and weak positivity for ER and PR. Mesoblastic nephroma is seen in a younger age group and is negative for ER and PR.[1],[3]

In malignant transformation, there is increased mitoses, necrosis, and cytologic atypia and rhabdoid, rhabdomyosarcomatous, and chondrosarcomatous differentiation may be seen.

Nephron-sparing surgery is the standard treatment and shows a favorable prognosis.

A subset of these patients may require continuous postoperative follow-ups to rule out possible malignant transformation.[4]

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Conflicts of interest

There are no conflicts of interest.

   References Top

Choy B. Mixed epithelial and stromal tumor. website. Available from:  Back to cited text no. 1
Mohanty SK, Parwani AV. Mixed epithelial and stromal tumors of the kidney: An overview. Arch Pathol Lab Med 2009;133:1483-6.  Back to cited text no. 2
Caliò, A, Eble JN, Grignon DJ, Delahunt B. Mixed epithelial and stromal tumor of the kidney. Am J Surg Pathol 2016;40:1538-49.  Back to cited text no. 3
Jung SJ, Shen SS, Tran T, Jun SY, Truong L, Ayala AG, et al. Mixed epithelial and stromal tumor of kidney with malignant transformation: Report of two cases and review of literature. Hum Pathol 2008;39:463-8.  Back to cited text no. 4

Correspondence Address:
Bharat Rekhi
Room Number 818, Department of Surgical Pathology, 8th Floor, Annex Building, Tata Memorial Hospital, Dr E.B. Road, Parel, Mumbai, Maharashtra - 400 012
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijpm.ijpm_310_22

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]


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