A novel sarcoma with dual differentiation: clinicopathologic and molecular characterization of a combined synovial...

We report on an unusual case of a 43-year-old woman who developed a malignant soft tissue tumor of the arm with overlapping morphology between synovial sarcoma (SS) and extraskeletal myxoid chondrosarcoma (EMC). The tumor recurred 7 years after the initial diagnosis and continued to demonstrate both SS and EMC histology. Immunophenotypically, the primary and recurrent tumors were both positive, focally, for cytokeratin, S-100, bcl-2, and epithelial membrane antigen. At the time of recurrence, the primary and recurrent tumors were further characterized for genetic and molecular abnormalities. Intriguingly, fluorescence in situ hybridization of the primary tumor revealed rearrangements of both the SS18 and EWSR1 genes. Furthermore, reverse transcriptase-polymerase chain reaction studies of both the primary tumor and the recurrence confirmed the presence of both SS18-SSX2 and EWSR1-NR4A3 (exon 3) gene fusions, characteristic of SS and EMC, respectively. This is the first reported case of a remarkable soft tissue sarcoma that exhibits overlapping morphologic features between SS and EMC and that also harbors a combination of SS18-SSX2 and EWS-NR4A3 gene fusions. This case supports the fact that specific, reproducible gene fusions frequently direct, cooperatively or competitively, basic histogenetic processes to produce tumor phenotypes.