Keratin-positive giant cell-rich tumor with HMGA::NCOR2 fusion in a 4-year-old.

Epiphyseal and metaphyseal bone lesions in pediatric patients are uncommon, and lesions that cross an open physis are even rarer. The differential diagnosis for such lesions consists of infection, giant cell tumor, and chondroblastoma. We describe a 4-year-old male patient who presented with a bone tumor originating in the proximal tibial metaphysis that extended across the physis into the epiphysis. Sampling revealed a HMGA2::NCOR2 fusion associated with a recently described subset of giant cell-rich bone and soft tissue tumors. This case expands the differential diagnosis for cross-physeal and epiphyseal bone tumors in pediatric patients and highlights the radiological features of keratin-positive giant cell-rich tumor (KPGCT).