Screening for potential targets for therapy in mesenchymal, clear cell, and dedifferentiated chondrosarcoma reveals Bcl-2 family members and TGFß as potential targets.

The mesenchymal, clear cell, and dedifferentiated chondrosarcoma subtypes are extremely rare, together constituting 10% to 15% of all chondrosarcomas. Their poor prognosis and lack of efficacious treatment emphasizes the need to elucidate the pathways playing a pivotal role in these tumors. We constructed tissue microarrays containing 42 dedifferentiated, 23 clear cell, and 23 mesenchymal chondrosarcomas and performed immunohistochemistry to study the expression of growth plate-signaling molecules and molecules shown to be involved in conventional chondrosarcoma. We observed high expression of SOX-9 and FGFR-3, as well as aberrant cellular localization of heparan sulfate proteoglycans, in all subtypes. TGFß signaling through p-SMAD2 and PAI-1 was highly active in all chondrosarcoma subtypes, which suggests that TGFß inhibitors as a possible therapeutic strategy in rare chondrosarcoma subtypes. As in conventional chondrosarcoma, antiapoptotic proteins (Bcl-2, and/or Bcl-xl) were highly expressed in all subtypes. Inhibition with the BH-3 mimetic ABT-737 rendered dedifferentiated chondrosarcoma cell lines sensitive to doxorubicin or cisplatin. Our data indicate that antiapoptotic proteins may play an important role in chemoresistance, suggesting a promising role for targeting Bcl-2 family members in chondrosarcoma treatment, irrespective of the subtype.

Sox9, a master regulator of chondrogenesis, distinguishes mesenchymal chondrosarcoma from other small blue round cell tumors.

Over the last decade, a number of "master regulator" genes that control distinct pathways of mesenchymal differentiation have been discovered. These genes are expressed early during embryogenesis and initiate a cascade of gene expression responsible for specific cell lineage commitment. Thus, identification of their products may allow the classification of seemingly primitive, morphologically uncommitted tumors such as small blue round cell tumors. The transcription factor Sox9 has been demonstrated to be a master regulator of the differentiation of mesenchymal cells into chondrocytes. For this reason, we examined the utility of Sox9 in distinguishing mesenchymal chondrosarcoma (a small cell malignancy thought to be derived from primitive chondroprogenitor cells) from other primitive small cell malignancies. Representative sections from 90 cases of small blue round cell tumors (22 mesenchymal chodrosarcoma, 10 neuroblastomas, 11 rhabdomyosarcomas, 9 Ewing's sarcomas/primitive neuroectodermal tumors, 5 desmoplastic small round cell tumors, 7 small cell carcinomas, 6 Merkel cell carcinomas, 6 small cell osteosarcomas, 7 diffuse large B-cell lymphomas, 7 lymphoblastic leukemias/lymphomas, and 5 extraskeletal myxoid chondrosarcomas) were immunohistochemically stained with antibodies to Sox9 protein. All but 1 mesenchymal chondrosarcoma showed positive nuclear staining in both primitive mesenchymal and cartilaginous components of the tumor. All other types of small blue round cell tumors, as well as the lymphomas and leukemias, were negative for Sox9 protein. These findings confirm that mesenchymal chondrosarcoma has phenotypic features corresponding to the early condensational phase of cartilaginous differentiation. More important, Sox9 may serve as a useful tool in the differentiation of small cell malignancies.

A mesenchymal chondrosarcoma of a child with the reciprocal translocation (11;22)(q24;q12).

The reciprocal translocation (11;22)(q24;q12) was observed in a seven day culture from a mesenchymal chondrosarcoma of the bone, a tumor not characterized cytogenetically so far. We suggest that because of the presence of a similar cytogenetic abnormality, mesenchymal chondrosarcoma may belong to the wide group of "t(11;22)-small round cell tumors".