SIMULTANEOUS INTERPHASE CYTOGENETIC ANALYSIS AND FLUORESCENCE IMMUNOPHENOTYPING OF DEDIFFERENTIATED CHONDROSARCOMA - IMPLICATIONS FOR HISTOPATHOGENESIS

Cytogenetic analysis of four specimens (biopsy, definitive surgical, a nd two separately occurring lung metastases) of a dedifferentiated cho ndrosarcoma with a rhabdomyosarcomatous component revealed clonal kary otypic abnormalities in each. Anomalies seen ill all specimens include d a structurally aberrant chromosome 17 and extra copies of chromosome s 5, 7, 12, and 20. The derivation of the chromosomally abnormal cells was determined by a combined immunocytochemical/cytogenetic approach that allowed simultaneous assessment of cytogenetic aberrations and im munophenotypic features of individual cells. S-100 protein and desmin antibodies were used to evaluate the chondrosarcomatous and rhabdomyos arcomatous components, respectively. A chromosome 7-specific centromer ic probe was used for determination of aneuploidy. In both specimens o btained from the primary lesion, S-100 protein and desmin-positive and -negative aneuploid cells were observed. These findings: 1) suggest th at both the chondrocytic and rhabdomyoblastic cells arose from the sam e abnormal clone, 2) support the theory of a common primitive mesenchy mal cell progenitor with the ability to differentiate or express featu res of more than one line of mesenchymal differentiation, and 3) indic ate that the term dedifferentiated may be an inaccurate designation fo r this neoplasm.