Dedifferentiated Liposarcoma of Soft Tissue with High-Grade Osteosarcomatous Dedifferentiation

History A 59-year-old white woman presented with a painless soft-tissue mass of the left thigh that had been progressively enlarging for about 6 months. At physical examination, the left distal thigh was markedly larger than the right. The large firm mass was noted along the medial aspect of the left distal femur. The remainder of the physical examination findings were fairly unremarkable. Her medical history was significant for breast cancer, seizure disorder, diabetes mellitus, hypertension, and hypercholesterolemia. Results of laboratory evaluation including white blood cell count, electrolyte level, hemoglobin and hematocrit levels, platelet count, and liver function studies were all within normal limits.