Keywords Breast · EosinophiliaSir, the presence of eosinophils encountered in female genital organs has been the subject of little attention. Their appearance in such tissues is considered to be an occasional accompaniment of a non-specific inflammation. In mammary tumors, eosinophilic inflammatory reaction has not been described as a peculiar feature. We describe a unique case of a fibroepithelial breast tumor with a striking eosinophilic infiltration in a 29-year-old female who had been taking oral contraceptives. A mammographic study showed a well-delimited nodule in her left breast. A fine-needle aspiration biopsy (FNAB) was performed, and a diagnosis of fibrocystic disease was rendered. The patient did not receive any intra-mammary injection of antibiotics or other medicaments during the FNAB. A chest X-ray was normal, as was her hematological profile. History of allergy and parasitic infestation was denied.Nine months later, the nodule was surgically removed. On gross examination, the nodule measured 1 cm in diameter and at cut surface exhibited a central solid tan-colored area with cystic spaces containing fluid at the periphery. Microscopically, the lesion showed biphasic architecture (Fig. 1). The stromal component was monomorphic and fibrous, with bland nuclear features and contained a polymorphous inflammatory cell infiltrate of lymphocytes, plasma cells, histiocytes and a striking number of eosinophils, particularly in the periphery of the cysts (Fig. 2). The epithelial component showed small cysts lined by hyperplastic epithelium and apocrine metaplasia. The epithelial cells showed increased proliferative activity with scattered typical mitoFig. 1 Low-power view showing a nodular appearance of the fibroepithelial lesion containing microcysts with micropapillary projections. Note the striking inflammatory stromal reaction rich in eosinophils. Hematoxylin and eosin ×100 Fig. 2 The epithelium component shows hyperplasia and intermixed eosinophils. The stroma shows a heavy inflammation. Hematoxylin and eosin ×200