MiT family translocation renal cell carcinoma after malignant infantile osteopetrosis in childhood: a case report.

Malignant infantile osteopetrosis (MIOP) is a rare inherited bone metabolism disorder characterized by increased bone mineral density (BMD) and abnormal hematopoiesis. Hematopoietic stem cell transplantation (HSCT) is currently the only curative therapy for MIOP. However, a higher risk of secondary malignancy occurs in children previously exposed to cytotoxic drugs. Here we report a rare case of a 3-year-old female patient with MiT family translocation renal cell carcinoma (MiTF tRCC), who is a survivor of HSCT for MIOP 2 years earlier. The patient had a complete resection of the tumor. Microscopically, we detected diffusely and papillary-like arranged tumor cells whose cytoplasm was bright and clear. Immunohistochemistry showed tumor cells diffusely expressed TFE3, and fluorescence in situ hybridization (FISH) demonstrated disruption of the TFE3 locus, confirming the diagnosis of Xp11 translocation RCC, the subtype of MiTF tRCC. This case supports the view that chemotherapy exposure is a risk factor for MiTF tRCC and indicates the possible association of HSCT with MiTF tRCC. IJCEP