Epidermal Inclusion Cyst: A Rare Benign Breast Lesion

Epidermal inclusion cyst in the breast is an uncommon condition. It may be congenital, originating from hair follicles or occurring after trauma (breast reduction or breast cytology puncture) or consists of squamous metaplasia of the regular columnar epithelium within an ectatic ductus galactophorus. We report the case of a 22-year-old woman, with two pregnancies and with no particular pathological history, who presented with a 3 cm nodule of the right breast at the union of the upper quadrants, firm, mobile and painless. The skin, areola and nipple were unaffected. The axillary areas and the contralateral breast were unremarkable. The breast ultrasound showed a heterogeneous and well circumscribed hypoechoic mass classified as ACR3. Macroscopic examination revealed a unilocular cyst with a discretely thickened wall, abundant yellowish contents and measuring 2 cm on a long axis. Histologically, it was a cystic cavity whose wall was lined with a pseudo stratified keratinized squamous epithelium with a granular layer and whose lumen contained keratin lamellae. This cyst is surrounded by a more or less fibrous pallial tissue containing regular, sometimes dilated or even cystic milk ducts. The diagnosis of epidermal inclusion cyst of the breast on a background of fibrocystic mastopathy was thus concluded. The importance of this benign lesion lies in the differentiation between other non-neoplastic and neoplastic breast lesions.