Mixed epithelial and stromal tumor (MEST) (pathology)

Case contributed by Dr Andrew Ryan


Complex renal cyst on imaging.

Patient Data

Age: 50 years
Gender: Male

Partial nephrectomy specimen with overlying perinephric fat (transverse section)


The partial nephrectomy specimen confirmed a multilocular cystic lesion, 15 x 12 x 12 mm

The sections show a multilocular cystic lesion, arising from the renal cortex. The lesion bulges into but shows a circumscribed interface with the perinephric fat.

The lesions is multilocular with intervening areas of cellular stroma.

Variably sized epithelial lined tubules and cysts surrounded by fibromuscular stroma. 

Columnar surface epithelium overlying cellular fibromuscular stroma.

The stroma characteristically shows positive staining for ER

Case Discussion

This is an example of mixed epithelial and stromal tumor (MEST), a benign mixed mesenchymal and epithelial neoplasms of the kidney. The tumor is composed of dilated tubules and cysts lined by a simple layer of epithelium, often with surface 'hobnail' outline, surrounded by variably fibrous to spindled to muscular stroma, often described as 'ovarian-like stroma'.

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