Histological Dedifferentiation in Recurrent Adamantinoma of the Tibia: A Case Report.

Introduction: Adamantinoma is a primary low-grade malignant bone tumor. It is most common in tibia with slight predilection in males. Dedifferentiated adamantinoma is an aggressive variant with worse prognosis. Case Report: Patient is a 70-year-old female who presented with leg pain. Imaging showed a lytic lesion in the metaphyseo diaphyseal region. Curettings were done and were reported as adamantinoma. Two years later, the patient presented with a recurrent lesion at the same site. Histopathology showed a neoplasm with focal classical adamantinoma and many areas with aggressive morphology including sarcomatoid differentiation. The neoplastic cells in high-grade areas were positive for vimentin with variable loss of cytokeratin. Proliferative index as determined by Ki67 was 20-25% in these areas. With these given immuno-morphological findings, a diagnosis of dedifferentiated adamantinoma was rendered. Conclusion: Dedifferentiated adamantinoma is an unusual and aggressive variant of adamantinoma. This case highlights the awareness of such a rare entity, thereby preventing misdiagnosis and improper treatment.