Epithelial inclusion cyst arising in an intramammary lymph node: case report with cytologic findings.

The occurrence of epithelial inclusion cysts (EIC) in axillary lymph nodes is a rare but well recognized entity, arising either from direct implantation or from embryonal rests. Theoretically, EIC can occur in intramammary lymph nodes, but there has been only one prior report of such a lesion. Here, we describe a case of an EIC arising in an intramammary lymph node of a 37-year-old woman. This report focuses on the FNA cytologic features of this lesion and its differential diagnoses. On FNA, the EIC arising in an intramammary lymph node was characterized by mature lymphocytes, squamous epithelial cells, and keratinizing material. The presence of squamous cells can lead to the erroneous diagnosis of more common breast lesions, such as squamous cell carcinoma or metaplastic carcinoma. Contrary to these more sinister diagnoses, EIC arising in an intramammary lymph node is a benign condition. As this rare lesion sometimes mimics a neoplasm both clinically and radiographically, awareness of this entity is important to prevent over treatment.