Extraskeletal Ewing's Sarcoma/Primitive Neuroectodermal Tumor of the Breast in a Young Woman.

Extraskeletal Ewing's sarcoma/primitive neuroectodermal tumors (EES/PNET) of the breast are rare malignant soft-tissue tumors associated with a high recurrence rate. We present the case of a 17-year-old female who presented with a lump in the left breast. Ultrasonography and mammography revealed a large, ill-defined, hypoechoic, heterogeneous, dense lobulated lesion without calcifications. Fine needle aspiration cytology showed atypical cells. Computed tomography of the brain, chest, and abdomen ruled out extra-mammary origin and metastasis. Wide local excision of the lesion followed by histopathological and immunohistochemical analyses confirmed the diagnosis of primary EES/PNET of the breast. The patient underwent adjuvant chemotherapy. Early diagnosis and multidisciplinary treatment are essential to improve prognosis and survival rates.