Cytogenetic finding:
46,XX,t(X;18)(p11.2;q11.2),inv(4)(p12q21)

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Karyotype of a cell from a patient with a spidle cell tumor on her arm. A portion of the tumor was finely minced and the cells were set up in culture. The cultured cells were harvested after growing for 5 days. The cells in mitosis were analyzed for chromosome number and structure. In 19 cells there was a balanced reciprocal translocation involving the short arm of an X chromosome and the long arm of a chromosome #18, with break points at band Xp11.2 and band 18q11.2. In addition, there was a pericentric inversion of a chromosome #4 with breakpoints at 4p12 and 4q21. The translocation between chromosomes X and 18 is highly characteristic of synoviosarcomas; this translocation (or a variation of it) has been found in more than 90% of reported cases. Synoviosarcoma is a malignant growth of the synovial cells in the joints and tendon sheaths.

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See the schematic of t(X;18)