Sections show an infiltrative, high-grade intramedullary tumor characterized by a hypercellular proliferation of markedly pleomorphic spindle to epithelioid cells. These cells exhibit marked cytological atypia, hyperchromasia, prominent nucleoli, and brisk mitotic activity with frequent atypical forms. Areas of tumor cells directly depositing abundant, disorganized, lace-like malignant osteoid and irregular woven bone trabeculae are observed. Confluent areas of geographic coagulative tumor necrosis are noted.
Large, aggressive proximal tibial bone lesion with extensive soft tissue involvement and neurovascular encasement.
Soft tissue and bone fragments collectively measured 5.5x4.5x1.5 cm, totally embedded.
Right proximal tibia lesion, biopsy: