52. Mixed epithelial and stromal tumour of kidney with prominent growth into pelvicaliceal system mimicking urothelial carcinoma

Abstract

Mixed epithelial and stromal tumour (MEST) of the kidney is rare neoplasm with low malignant potential, most commonly found in middle-aged women who had long-term history of oestrogen replacement. With complete surgical excision of the tumour the outcome is usually favourable. Nonetheless a few cases of malignant transformation of the stromal component have been described in recent literature. The unusual case of MEST was encountered in our department with prominent vegetation into pelvicalyceal system suggestive papillary urothelial neoplasm, which was the preoperative diagnosis. However microscopic examination showed typical for MEST biphasic tumour with marked growth under reactive urothelium. Immunostains of the renal neoplasm showed positive staining of epithelial cells with CK7, AE1/AE3, PAX8, weak staining with CD10 and S100, Ki67 low labelling. It also revealed strong staining of Stromal cells with CD10, ER, PR and Smooth Muscle Actin with negative staining for MelanA, HBM 45, S100 and Ki67 low labelling. Histogenesis of mixed epithelial and stromal tumour of kidney remains questionable. It is believed that both components of tumour are neoplastic with possibly common cell of origin. As mentioned above, surgical excision is curable in most of the cases, however malignant transformation is possible and the definition of malignancy is problematic in this entity.