A biphasic pattern is seen with a well-differentiated cartilage and a small blue cell malignancy in varying proportions. Usually, the two components are sharply delineated, but blended transitions may also occur. The small cells have ovoid hyperchromatic nuclei and may be surrounding staghorn-shaped vessels often seen in hemangiopericytomas.The transition between the two components is usually abrupt, but may be gradual in some areas.
The cartilage usually appears benign, but is considered a well-differentiated chondrosarcoma.
The small blue cells are hyperchromatic with round to ovoid nuclei and relatively little cytoplasm.
Although not well-demonstrated here, the small cells often surround staghorn-like branching vascular spaces reminiscent of a hemangiopericytoma.
Sheets of small dark blue cells arising in the bone of a young patient can elicit concern for an Ewing sarcoma. However, chondroid areas are not present in Ewing sarcoma -- and mesenchymal chondrosarcomas do not exhibit the characteristic chromosomal translocation seen in Ewing sarcoma. Although the small cell component can express CD99 similar to Ewing sarcoma, mesenchymal chondrosarcoma do not exhibit the t(11;22) EWS:FLI1 translocation (Folpe).
The transition from one area to another is seen here again. There is a tendency to involve the jaws and ribs. One-third of cases arise in extraosseous sites such as soft tissues or meninges (Folpe, Fletcher).
Mesenchymal chondrosarcoma affects a younger set of patients i.e. adolescents and young adults, versus a peak incidence in the fourth to sixth decades in conventional chondrosarcoma.
Excision, reconstruction and limb-sparing surgery (if possible).
Some present at advanced stage and die in a few months whereas others may survive a long while before disseminated disease occurs. Long-term prognosis is poor.
Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 1612-3.
Folpe AL, Inwards CY. Bone and Soft Tissue Pathology: Foundations in Diagnostic Pathology Philadelphia, PA: Elsevier; 2010: 350-2.