Adamantinoma-like Ewing's sarcoma: Genomic confirmation, phenotypic drift

Ewing's sarcoma, a highly malignant neoplasm, is characterized by an 11;22 translocation [t(11;22) (q24;q12)], resulting in the fusion of genes FLI1 a nd EWS. Adamantinoma of extragnathic bones, a low-grade malignant neoplasm with epithelial features, is not typically considered in the differential d iagnosis of Ewing's sarcoma. In this study, three osseous Ewing's sarcomas with histological, immunohistochemical, or ultrastructural epithelial featu res were subjected to reverse transcription-polymerase chain reaction and s equencing studies for the Ewing's sarcoma molecular rearrangement. (Two of the three cases were originally described as adamantinomas or nontypical Ew ing's sarcoma before the availability of genetic characterization.) In addi tion, traditional cytogenetic analysis and a unique combined interphase mol ecular cytogenetic/immunocytochemical approach with bicolor 11;22 transloca tion breakpoint flanking probes (cosmids) and pancytokeratin antibodies wer e performed on one neoplasm. A t(11;22) (q24;q12) was found in one neoplasm and a type II EWS/FLI-1 fusion transcript was detected in all three neopla sms. The combined genetic/immunocytochemical approach revealed the presence of the 11;22 translocation in the nuclei of cytokeratin immunoreactive cel ls. These genotypic and phenotypic findings delineate a novel Ewing's sarco ma histologic variant, "adamantinoma-like Ewing's sarcoma."