MDM2-positive papillary sarcomatoid renal cell carcinoma: a potential diagnostic pitfall.

Sarcomatoid renal cell carcinoma is a highly aggressive form of carcinoma, histologically showing both carcinomatous and mesenchymal component in different proportions. We present a case of advanced type 1 papillary sarcomatoid renal cell carcinoma infiltrating adjacent organs and showing positivity for MDM2 by immunohistochemistry and MDM2 amplification by fluorescence in situ hybridization. This finding, together with sarcomatoid morphology, poses a potential pitfall for diagnosis with dedifferentiated liposarcoma. MDM2 is known to be altered in various human sarcomas. Only recently, MDM2 alterations have been reported in carcinomas. The presented case illustrates the need of thorough sampling with clinic-pathological correlation before making a final diagnosis in sarcomatoid retroperitoneal tumours. Additionally, the potential clinical implications of MDM2 amplification in renal cell carcinoma are discussed.