The biopsies show a chondroid neoplasm. It is mildly hypercellular, containing lobules of cartilage. The chondrocytes have focal mild nuclear enlargement and hyperchromasia. Occasional binucleated forms are seen. There are no mitoses or necrosis. Some of the cartilage are surrounded by host bone. An invasive growth pattern is noted although no definite invasion through the bone is seen. The lesional cells are S-100 and M2A positive, confirming chondroid differentiation. They are CAM5.2 negative, excluding chordoma.
DIAGNOSIS: Grade 1 chondrosarcoma.