We analyzed the clinicoradiographic, microscopic, and immunophenotypic features of 21
tumors from 13 patients with
mesenchymal chondrosarcoma (11 primary and 10 metastatic) and addressed the issue of their potential polyphenotypic differentiation. The immunophenotypic profile of the
tumors was analyzed by studying the expressions of the MIC2 gene
protein (p30/32(MIC2)),
S-100 protein,
desmin, myoD1,
myogenin,
myoglobin, smooth-muscle actin,
cytokeratin,
neuron-specific enolase, and HMB-45. The expression of p30/32(MIC2) was typically restricted to the small cell component of the
mesenchymal chondrosarcoma and could be documented in 17
tumors. The cartilaginous areas were positive for
S-100 protein in 20
tumors. Scattered positivity of small cells for
desmin was seen in 8 cases. In 2 primary
tumors from different patients (1 intraosseous and 1 extraskeletal) a diffuse expression of
desmin with focal coexpression of myoD1 was present within the small cell component of the
tumor. The positivity for smooth-muscle actin was documented in 2 cases. Either the small cell or cartilaginous components were at least focally positive for
neuron-specific enolase in 11
tumors. All
tumors were negative for
myogenin,
myoglobin, cytokeratins (AE1/AE3,
CAM5.2) and HMB-45. This study showed that, in addition to cartilaginous differentiation,
mesenchymal chondrosarcomas may exhibit focal expression of
desmin. In rare cases more diffuse rhabdomyoblastic differentiation can be seen within the small cell component of the
tumor. Thus,
mesenchymal chondrosarcoma is another primitive
neoplasm with polyphenotypic differentiation and features that overlap those of other small cell malignances of bone and soft tissue. Int J Surg Pathol 8(4):291-301, 2000