Analysis of chromosome 22q as an aid to the diagnosis of rhabdoid tumor: a case report.

Malignant rhabdoid tumor is a highly aggressive tumor of childhood that may present as a soft-tissue primary tumor. We report a soft-tissue neoplasm that was polyphenotypic by immunohistochemical expression of epithelial, mesenchymal, and neural markers and did not meet the criteria for any of the usual pediatric small round-cell tumors. The findings raised the diagnosis of rhabdoid tumor, leading to testing for WT1 mRNA and protein expression, which were positive, as has been reported for renal rhabdoid tumor. This tumor had the typical clinical behavior of rhabdoid tumor with therapy resistance and early tumor-related death. Multicolor spectral karyotyping of this neoplasm showed a balanced translocation between chromosomes 1 and 22 with breakpoints at 1p36 and 22q11-12. The latter region is commonly involved in rhabdoid tumor. This change was also identified by fluorescence in situ hybridization. This case suggests that studies of chromosome 22 may be required to distinguish rhabdoid tumor from other soft-tissue tumors.