an epidermal inclusion cyst refers to a cyst that results from the proliferation and implantation of epidermal elements within a circumscribed space in the dermis . histopathologically , these lesions are formed by inclusion of keratinizing squamous epithelium within the dermis resulting in a cyst filled with lamellated keratin . a 47-year - old female was admitted with a complaint of a large palpable mass in the left breast . physical examination revealed an over 8 cm sized large subareolar lesion of the left breast which appeared to be a firm , well - described mass , attached to the skin . abnormal laboratory findings were not observed with a normal range of complete blood count and c - reactive protein . mammography showed a round , dense , smoothly outlined mass measuring 7  6 cm ( fig . breast sonography showed a solid , hypoechoic with heterogeneous internal echoes and well demarcated border ( fig . therefore , we presumed a large fibroadenoma or phyllodes tumor , or benign features of a malignant lesion such as mucinous carcinoma due to the overly large size . a fine needle aspiration biopsy was done and a thick yellowish viscid material with offensive odor was aspirated during the biopsy thus confirming the cystic nature of the lesion . however , we could not get adequate biopsy material due to too its thick nature and the mass was still palpable . the giant size and breast location of the palpable mass was causing the patient 's discomfort , and the mass size had grown gradually over the past month . moreover , there was clinical concern for possible underlying malignancy due to the overly large sized mass , and the mass had a potential risk of malignant transformation . the histology of the specimens showed a cyst lined by mature stratified squamous epithelium filled with laminated keratin along with a cholesterol cleft surrounded by a giant cell and histiocytes suggesting a microruptured cyst ( fig . 3 ) . based on these data , we established the diagnosis as a micro - ruptured epidermal inclusion cyst in the breast . at the follow - up examination 8 months postoperatively , the patient was asymptomatic and there was no local recurrence of the lesion . in summary , we encountered a rare case of a giant - sized epidermal inclusion cyst of the breast that initially mimicked a large fibroadenoma or phyllodes tumor . epidermal inclusion cysts are common cutaneous benign inflammatory lesions , and have been found in various parts of the body that are usually located in the face , scalp , neck , and trunk . only a few cases of epidermal cysts of the breast have been reported in the literature and most of these cases are small in size except 1 case where the reported size was 9  8 cm . furthermore , a larger than 7 cm large size epidermal inclusion cyst in the breast has not been reported in korean literature . epidermal inclusion cysts have been referred to by various terms including : follicular infundibular cysts , epidermal cysts , and epidermoid cysts . the term epidermal inclusion cyst refers specifically to an epidermoid cyst that is the result of the implantation of epidermal elements in the dermis . there is no definitive understanding of how epidermal inclusion cysts actually develop , however a few theories of their etiology have been postulated . firstly , epidermal inclusion cysts can be congenital , arising from cell nests remaining from cells such as the embryonal mammary ridge . thirdly , epidermal inclusion cysts may result from trauma , such as reduction mammoplasty or needle biopsy of the breast . these procedures may cause epidermal fragments to be implanted more deeply within the breast tissue and a concurrent stimulation of epithelial proliferation . fourthly , pilosebaceous structures may become inflamed , leading to a cystic reaction in the dermis . this theory is typically used to explain the presence of cysts on the face , neck , and trunk . finally , epidermal inclusion cysts may be created by squamous metaplasia of normal columnar cells within a dilated duct in the case of fibrocystic disease or in a fibroadenoma or phyllodes tumours . most breast epidermal inclusion cysts occur in the skin layer and physical examination revealed a firm , well described , and small mass . the mammography appearance of epidermal inclusion cyst in the breast typically appears to be well circumscribed with homogeneous increased density . the sonographic appearance of epidermal inclusion cyst in breast may have a solid , well - circumscribed and complex or heterogeneous appearance . some reports described the specific sonographic features of these lesions such as an onion ring appearance with alternating concentric hyperechoic and hypoechoic rings containing lamellated keratin , while other reports described cysts with extension into the dermis . magnetic resonance imaging analysis of epidermal inclusion cysts showed a fluid - like signal with variable low - signal components on t2-weighted images and peripheral rim enhancement on gadolinium - enhanced images . an epidermal inclusion cyst of the breast can result in several problems even if the size is unusual . first , spontaneous rupture of the large epidermal inclusion cyst may occur releasing nonabsorbable keratin that acts as an irritant leading to secondary foreign body reactions , granulomatous reactions or abscess formation . more over , an association between epidermal inclusion cyst and squamous cell carcinoma has been reported . but incidence of malignant potential is extremely variable ( 0.045 to 19% ) and true incidence is uncertain . finally , a large sized cyst in the breast parenchyma should be evaluated using the differential diagnosis of a large fibroadenoma or phyllodes tumor , or even as a malignant breast lesion with benign features such as mucinous carcinoma . furthermore , biopsy is unnecessary if typical sonographic , mammographic , and clinical findings are found . however , epidermal inclusion cysts , especially palpable breast masses in women and large sized lesions that may cause patient discomfort physically and psychologically , require surgical excision . entire cyst wall removal is recommended for both pathologic confirmation , such as a malignant lesion with benign imaging findings , and for the prevention of potential risks of recurrence ( about 3% ) , inflammation , and malignant change .
epidermal inclusion cysts are formed by inclusion of keratinizing squamous epithelium within the dermis , resulting in a cyst filled with lamellated keratin . 
 these benign cysts are usually very small and intradermal subcutaneous lesions . 
 they can occur anywhere in the body although they are more common on the face , trunk , neck , extremities and scalp . 
 only a few cases of epidermal cysts of the breast have been reported in the literature . 
 an epidermal inclusion cyst of the breast can result in several problems , even if the size is unusual . 
 we encountered a case of a giant sized epidermal inclusion cyst of the breast initially mimicking a large fibroadenoma or phyllodes tumor .