Sandbox: Bone DDx

• 20-30 yo female
• Bone pain and swelling
• Pathologic fracture
• Paget disease of bone

• Localised bone tenderness

• Epiphyses of the long bones
• Solitary expansile eccentrically-placed lytic lesion
• Intratumoral hemorrhage present
• Tumor extends into the subchondral plate

• Uniform and regular distribution of multinucleated giant cells and mononuclear stromal cells
• Hemorrhage, necrosis, and hemosiderin deposition
• Elevated mitotic figures

acid phosphatase +ve alpha-1-antitrypsin +ve alpha-1-antichymotrypsin +ve Ki-67 +ve