Abstract
Extraskeletal Ewing's sarcoma (EES) is a rare soft tissue tumor predominantly observed in adolescents and young adults, and is characterized by aggressive behavior. So far, only two cases of primary axillary soft tissue EES have been reported in the literature. One of them was a 29-year-old female patient who presented with a lump in her left axilla. Upon examination, an irregular, painless mass, measuring 5 cm x 5 cm x 3 cm, was noted in the left axilla. A histopathological examination of the mass revealed small, round, blue cells with scant cytoplasm, round nuclei, numerous mitosis, and necrosis. An immunohistochemistry (IHC) examination was positive for CD99 and negative for ER, PR, Her2neu, CK7, CK5/6, CD56, CD45, CK-pan, CKHMW, P63, desmin, S100, TdT, vimentin, myogenin, synaptophysin, and chromogranin A. The patient was diagnosed with primary axillary soft tissue EES and was started on neoadjuvant chemotherapy. Twelve months later, she is clinically free from the disease.