Adamantinoma of the Femur With High-Grade Epithelial and Sarcomatoid Components: Case Report and Review of the Literature

Adamantinomas are rare low-grade malignant bone tumors that are composed of epithelial cells set in an osteofibrous stroma. Osteofibrous dysplasia-like and classic forms are well known; however, sarcomatous transformation (dedifferentiation) is very rarely observed. We present the case of a 48-year-old woman who presented with a 5-cm proximal femoral lytic lesion at risk of pathologic fracture. Frozen-section evaluation demonstrated an intimate admixture of atypical squamous nests and spindle cells, consistent with metastatic sarcomatoid carcinoma, so prophylactic intramedullary nailing was completed. Postoperative clinical and radiologic evaluation failed to identify a primary carcinoma, and short-term follow-up demonstrated rapid tumor spread throughout the femur and thigh. The patient underwent hip disarticulation, and microscopic examination demonstrated areas of classic adamantinoma associated with both high-grade epithelial and sarcomatoid components. Diffuse metastatic spread was evident within seven months. Along with a description of this case, we review the clinical, radiographic, histologic, and immunophenotypic characteristics of the eight adamantinomas with high-grade sarcomatous transformation that have been previously reported in detail in the English literature, and discuss important considerations for differential diagnosis.