INTRODUCTIONSarcomas are heterogeneous, and their treatment and prognosis are driven by the morphologic subtype and the clinical stage. Classic cytogenetics and fluorescence in situ hybridization (FISH) analysis play an important role in their diagnostic work up.MATERIALS AND METHODSForty-six cases of soft-tissue sarcoma were reviewed that underwent karyotyping and simultaneous FISH analysis at initial diagnosis. They included 10 dedifferentiated liposarcomas, 10 myxoid liposarcomas, and 14 synovial sarcomas. Six tumors were investigated for EWSR1 rearrangement. Six high-grade miscellaneous sarcomas were also examined.RESULTSThe dedifferentiated liposarcoma had complex karyotypes and MDM2 amplification by FISH, and of these, 5 tumors with myxoid changes also had complex signals for DDIT3. All but 4 myxoid liposarcomas had complex karyotypes, in addition to the characteristic translocation. FISH analysis displayed DD1T3 rearrangement. All synovial sarcomas except 1 recurrence had a t(X;18) translocation by karyotyping and FISH. The EWSR1 rearrangement was present in all extraskeletal myxoid chondrosarcomas, angiomatoid fibrous histiocytoma, atypical Ewing sarcoma, and a clear-cell sarcoma, all of which had characteristic karyotypes. Seven high-grade sarcomas had no specific karyotype or rearrangements for DDIT3, SS18, and EWSR1 by FISH.CONCLUSIONSThere is good correlation between karyotyping and FISH. Complex FISH signals found in dedifferentiated liposarcomas may be related to an increased chromosome 12 copy number and ploidy. Karyotyping is an important baseline standard for the quality assurance of newly developed FISH probes. It also provides a global view of chromosomal changes and the opportunity to investigate the role of other genetic alterations and potential therapeutic targets.