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.
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Epidemiology
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.
Clinical presentation
Most are incidental findings. Can also present as palpable abdominal or flank mass, flank pain, and/or hematuria.
Pathology
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.
Radiographic features
CT
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.
Treatment and prognosis
They are almost universally benign, however, rare cases with malignant transformation, recurrence, and metastasis have been reported 1,6.
Differential diagnosis
- multilocular cystic renal neoplasm of low malignant potential, formerly multilocular cystic renal cell carcinoma 7
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