Periosteal Chondrosarcoma

The Union for International Cancer Control (UICC) TNM classification does not recommend applying the TNM staging system for bone tumors to surface/juxtacortical chondrosarcoma. However, other staging systems, such as the American Joint Committee on Cancer (AJCC) TNM system, do include these tumors in the bone staging system. See also the information on staging in section Bone tumors: Introduction.

A subset of periosteal chondrosarcomas bear the same IDH1 and IDH2 mutations as enchondroma and conventional central chondrosarcoma.

A large (often > 5 cm) lobulated mass is located on the surface of the bone. On cut section, the tumor is grey and glistening and is often associated with gritty white areas of calcification. The tumor erodes or invades the cortex; the medullary canal is usually not involved.

A lobular, moderately cellular cartilaginous tumor is seen with myxoid matrix. Calcification and endochondral ossification can be present. Osteoid or bone directly formed by the tumor cells is absent, although formation of metaplastic bone at the periphery of the cartilage lobules and the tumor (formation of a so-called neocortex) can be found. The features resemble those of atypical cartilaginous tumor / chondrosarcoma, grade 1 (ACT/CS1) or grade 2 central chondrosarcoma. There is often invasion of the underlying cortex. Intramedullary extension and subsequent host bone entrapment are seen in a subset of cases. Demarcation with the soft tissue is usually sharp.

Not clinically relevant

Periosteal chondrosarcomas have a relatively low metastatic rate (5–12.2%), with metastases especially involving the lungs and rarely the lymph nodes. Histological grading does not predict outcome.

Although IDH1 and IDH2 mutations are found in a subset of periosteal chondrosarcomas, mutation analysis is rarely used in the diagnostic work-up for periosteal chondrosarcoma. It might be used to distinguish periosteal chondrosarcoma and periosteal osteosarcoma, the latter being negative. The EXT1 protein is normally expressed, whereas RB1 signaling can be deregulated by the loss of p16 expression, and WNT/β-catenin signaling is lost in the majority of cases. Amplification of CDK4 or MDM2 is absent, unlike in parosteal osteosarcoma.

Essential: cartilaginous tumor arising on the surface of bone in close association with periosteum; invasion of the underlying cortex or size > 5.0 cm.