Mixed epithelial and stromal tumor

Mixed epithelial and stromal tumors (MEST) are a family of uncommon renal neoplasms in adults in a spectrum ranging from predominantly cystic (adult cystic nephroma) to more solid tumors. 

There is a female preponderance 10:1 1 with tumors occurring predominantly in middle-aged peri-menopausal women and older women. There is a possible link with estrogen therapy and other hormonal treatment, including GnRH agonists 2,5.

Most are incidental findings. Can also present as palpable abdominal or flank mass, flank pain, and/or hematuria.

This benign kidney tumor shows solid and cystic architecture and is composed of epithelial and mesenchymal elements 4-5:

  • the epithelial component is composed of dilated tubules and cysts lined by a simple layer of cuboidal to columnar epithelium, often with prominent surface 'hobnail' outline
  • the epithelium stains strongly for renal lineage markers (PAX8) and for CK7
  • the surrounding stromal component is fibrous to spindled to focally muscular and shows expression of ER and PR; it is often described as 'ovarian-type stroma'

The lesion is usually well circumscribed from the surrounding renal parenchyma and perinephric fat and lacks features of malignancy including invasive growth, necrosis or significant cellular atypia. 

It is typically seen as a multiloculated cystic renal mass with a variable proportion of solid and cystic components and containing internal septa. The latter may demonstrate heterogeneous and delayed contrast material enhancement 3.

They are almost universally benign, however, rare cases with malignant transformation, recurrence, and metastasis have been reported 1,6.

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Article information

rID: 26139
System: Urogenital
Tag: cases
Synonyms or Alternate Spellings:
  • Mixed epithelial and stromal tumor (MEST)
  • Mixed epithelial and stromal tumour of the kidneys
  • Mixed epithelial and stromal tumour of kidney
  • Mixed epithelial and stromal tumour of kidneys
  • Renal mixed epithelial and stromal tumour
  • Mixed epithelial and stromal tumor of the kidney
  • Mixed epithelial and stromal tumor of kidney

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Cases and figures

  • Figure 1: gross pathology
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  • Figure 2: low power histology
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  • Figure 3: histology
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  • Case 1
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