Ewing sarcoma of the head and neck: a histopathologic report of 3 cases

Ewing sarcoma is a highly aggressive malignancy of bone and soft tissues that primarily affects the long bones of children and young adults. Approximately 85% of Ewing sarcomas harbor the chromosomal translocation t(11;22), which produces the characteristic oncogenic fusion gene EWSR1::FLI1. Although head and neck Ewing sarcomas (HNESs) are rare and only few extraskeletal cases have been reported, these still present with the usual molecular, microscopic, and immunophenotypic features. This paper reports 3 cases of HNESs in the maxilla of a 71-year-old male, mandible of an 18-year-old female, and floor of the mouth of a 32-year-old male. Microscopically, the tumors consist of a monomorphic population of small round blue cells with indistinct cell borders, scant amounts of pale cytoplasm, and round to ovoid vesicular nuclei with finely dispersed chromatin. Immunohistochemistry reveals diffuse and strong membranous CD99 reactivity and nuclear positivity for NKX2.2 in the tumor cells. There have been 183 reported cases of HNESs, with the mean age at diagnosis of 25 years. The most commonly affected sites are bones of the skull and face (including maxilla) (40%), soft tissues (30%), and mandible (9%). HNESs are uncommon, especially in nonpediatric population but should be considered in the differential diagnosis for tumors composed of undifferentiated small round blue cells. Other tumors that share similar histology include rhabdomyosarcomas, lymphomas, neuroendocrine tumors, primary and metastatic, and BCOR- and CIC-rearranged sarcomas to name a few. Immunohistochemistry with CD99 and NKX2.2 and molecular studies help to differentiate between such tumors.