A, Anteroposterior view of right proximal humerus of 92-year-old woman with dedifferentiated chondrosarcoma shows aggressive-appearing area (arrows) adjacent to otherwise typical chondrosarcoma. B, Resected specimen shows these features. C, Typical microscopic appearance of dedifferentiated chondrosarcoma. High-grade spindle cell sarcoma is located adjacent to low-grade chondrosarcoma. D, Anteroposterior radiograph after reconstruction with endoprosthesis.