Adamantinoma-Like Ewingʼs Sarcoma: Usefulness of Genetic Approaches in Diagnosing Small Round Cell Tumors

Abstract

A 13-year-old boy had a painful longitudinal swelling over the lateral aspect of the right calf. Radiographic studies revealed a dense fibular diaphyseal lesion with an associated soft tissue mass interpreted as probable Ewing's sarcoma. In contrast to the expected small round cell tumor appearance, the biopsy tissue was composed of nests of hyperchromatic, mildly pleomorphic cells separated by a pronounced desmoplastic reaction. Immuno-phenotyping showed that the tumor cells were strongly keratinand vimentin-immunoreactive but negative for 0-13 (MIC2). Other epithelial-like features included the presence of abundant intermediate filaments (including tonofilaments) and complex desmosomal-type intercellular junctions. These histologic, immunohistochemical, and ultrastructural findings were consistent with a diagnosis of adamantinoma, an entity that is not usually considered in the differential diagnosis of Ewing's sarcoma. Genetic analysis of this patient's tumor specimen, in addition to two cases previously described in the literature as “Ewing-like adamantinomas,” revealed the presence of the 11;22 translocation [t(11; 22)(q24;q12)] and/or the associated EWS/FLI1 fusion transcript characteristic of Ewing's sarcoma and peripheral primitive neuroectodermal tumors. This case illustrates the diagnostic challenges often encountered in bone and soft tissue tumors. Recently, recognition of specific cytogenetic and molecular genetic abnormalities in these neoplasms has significantly reduced some of the associated difficulties and has provided valuable information with respect to histopathogenesis. A review of the diagnostic and prognostic usefulness of genetic studies in Ewing's sarcoma and peripheral primitive neuroectodermal tumors is presented.