Extraskeletal and Skeletal Myxoid Chondrosarcoma: A Multiparameter Analysis of Three Cases Including Cytogenetic Analysis and Fluorescence In Situ Hybridization.

Background: Myxoid chondrosarcoma (MCS) is a rare, low-grade, indolent tumor that can occur in soft tissue and bone. It is, however, capable of distant metastases. Previous cytogenetic data include a translocation, t(9;22)(q22-31;q12), occurring in 6 of 14 cases of the extraskeletal variant of the disease. Recently, rearrangement of the EWS gene has been reported in MCS. Methods and Results: Three cases of MCS, two skeletal and one extraskeletal, were examined to identify primary cytogenetic changes and correlate these with immunohistochemical, ultrastructural, and flow-cytometric analysis. The extraskeletal variant of MCS revealed a clonal translocation, t(9;22)(q22;q12), and trisomy for chromosomes 5, 7, 8, 12, 18, and 19. Our two cases of skeletal MCS showed complex karyotypes. In one skeletal tumor, a cryptic translocation involving chromosome 6p21.3 was identified by fluorescence in situ hybridization analysis, using chromosome-specific libraries. Conclusions: Thus far, 50% of cases of extraskeletal MCS, including our cases, have demonstrated a specific translocation, t(9;22)(q22-31;q12). Identifying this translocation is useful in confirming the diagnosis of MCS. Additional cytogenetic and molecular analysis is useful for detecting this translocation, and is also essential to determine other regions of possible diagnostic importance, such as the 6p21.3 breakpoint demonstrated in the present study. These techniques may be most useful for the skeletal lesions, in light of their heterogeneous cell populations and karyotypic variability.