Two case reports of mixed epithelial and stromal renal tumor of kidney in children and literature review analysis.

Mixed epithelial and stromal tumor of the kidney (MESTK) occurs almost exclusively in perimenopausal women while rarely in children. Only five pediatric patients have been described previously. Herein, we report a girl and a boy with MESTK, aged 3- and 4-years-old, respectively. The two patients presented with hematuria or an abdominal mass. Histologically, the tumors were both composed of epithelial and stromal elements. Immunohistochemical staining of tumor cells expressed epithelial and mesenchymal component markers. They were diagnosed with MESTK by histology and immunohistochemistry after surgery. The patients were at good condition after surgery. To our knowledge, these are the youngest reported cases of MESTK. And the glandular luminal structure formed by the epithelium was lined with urothelium, which expanded the histological map of MESTK.