Abstract
Ewing's sarcoma/primitive neuroectodermal tumors (EWS/PNET) are rare malignant and aggressive tumors, usually seen in the trunk and lower limbs of children and young adults. They are uncommon in the breast. We report a case of a 43-year-old woman who developed a painless breast mass. An initial core needle biopsy concluded to a fibrocystic dystrophy contrasting with a rapidly growing mass; thus a large lumpectomy was done. Diagnosis of primary PNET of the breast was established, based on both histopathological examination and immunohistochemical findings. Surgical margins were positive, therefore, left modified radical mastectomy with axillary lymph nodes dissection was performed. The patient was given 6 cycles of adjuvant chemotherapy containing cyclophosphamide, adriamycin and vincristine. Twenty months later, she is in life without recurrence or metastasis. EWS/PNET may impose a diagnostic challenge. Indeed, mammography and ultrasonography features are non specific. The histopathological pattern is variable depending on the degree of neuroectodermal differentiation. Immuno-phenotyping is necessary and genetic study is the only confirmatory tool of diagnosis showing a characteristic cytogenetic anomaly; t (11; 22) translocation.