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Discussion

Epidermal inclusion cysts are formed by inclusion of keratinizing squamous epithelium within the dermis, resulting in a cyst filled with lamellated keratin. These common benign lesions can occur anywhere but are most often found on the face, trunk, and neck. Neoplastic transformation within epidermal inclusion cyst is very rare. Fewer than 40 cases of epidermal inclusion cyst of the breast have been reported in the English-language literature [1–8]. Typical epidermal inclusion cysts appear as smooth, round nodules attached to the skin. It is not uncommon for breast epidermal inclusion cysts to be clinically misdiagnosed initially [1]. They usually appear as well circumscribed on mammography and solid on sonographic examination. Even when the mammographic appearance of a palpable mass is consistent with a benign lesion, the finding of a solid lesion on sonography may result in the need for a tissue diagnosis to exclude a carcinoma with well-defined borders. The sonographic appearance of breast epidermal inclusion cysts has been described as solid, circumscribed, and complex [3–6]. Denison et al.[5] describe specific sonographic features of breast epidermal inclusion cysts in their report of cysts with extension into the dermis.