Epidermal inclusion cyst in breast: Is it so rare?

BACKGROUND: Epidermal inclusion cyst in the breast (EICB) is very rare. It presents as breast lump mainly in peri-areolar region and needs to be differentiated from other breast lesions with predominance of squamous cells. AIM: To analyze the role of fine needle aspiration cytology (FNAC) in patients presenting with breast lump.
MATERIALS AND METHODS: The present study is a retrospective study over the period of past 2 years, where the patients presented with firm breast lumps. Six of these cases were diagnosed as EICB on FNAC. Smears from these cases were reviewed for cytomorphological findings and correlated with clinico-radiological details.
RESULTS: Patients ranged in age from 25 to 60 years, and female to male sex ratio was 2:1 (female 4, male 2). Mammography was done in women (4), which showed solid, well-defined mass lesions in peri-areolar region and were suggestive of benign breast lesions (3) and infective lesion (1). FNA was performed; Giemsa-stained smears showed predominantly mature benign squamous cell and anucleated squames in all cases, thus one of the cytological diagnoses was EICB. Five of these cases had histological confirmation.
CONCLUSION: EIC of breast is not that rare lesion as considered. The patients may not seek medical attention because of small painless swelling; unless the lump increases in size or becomes painful. FNAC is confirmatory in the presence of a typical pultaceous aspirate and cytomorphological features of EIC. Thus, FNAC plays a crucial role in its diagnosis and management. Symptomatic cases should be readily excised and need histological correlation to rule out any potential complications that can arise in these cysts.

Introduction

Epidermal inclusion cyst (EIC) refers to the cyst that results from proliferation and implantation of epidermal elements within a circumscribed space in the dermis. Such cysts can occur anywhere in the body, although they are more common in head and neck region, trunk, and extremities. The occurrence of EIC in the breast (EICB) is very rare; to date, less than 40 cases have been reported to the best of English literature search.[1-9] EICB presents as a small lump and needs to be differentiated from other non-neoplastic and neoplastic breast lesions. Published cytological literature on EIC in breast is scanty and there are only five reports.[410-13] We report six cases of EIC presenting as breast lumps, which were diagnosed initially on fine needle aspiration cytology (FNAC). The diagnostic difficulties encountered during cytological reporting of this lesion and the differential diagnosis (D/D) that should be kept in mind are also discussed.

Materials and Methods

The present study is a retrospective study over a period of past 2 years, where patients presented with breast lump and one of the cytological diagnoses was of EICB. Detailed clinico-radiological and cytohistological findings were reviewed. FNAC was performed in all six cases using 22-gauge disposable needles; aspirates were pultaceous in all, except one where it was purulent (Case 4); smears were processed as air-dried Giemsa-stained preparations. Cytomorphological features were suggestive of EIC as one of the D/D in all six cases due to the presence of many anucleated squames (AS) and nucleated benign squamous cells (NBSC). Histopathological diagnosis was available in four cases.

Results

Clinical details are provided in Table 1, and cytological findings, diagnosis and its correlation with radiological and histological diagnosis are shown in Table 2. There were four females and two males (F:M = 2:1), with age ranging from 25 to 60 years. Patients presented with breast lumps [left breast (3) and right breast (3)] ranging in size from 1.5 to 0.5 cm, which were firm, mobile, non-tender (3), tender (1), partially adhered to the overlying skin (5) and sinus discharging pus (1). There was no skin change, no nipple discharge (ND) or retraction. There was no history of trauma, previous surgery, breast infection, hormone intake or a family history of breast disease. Contralateral breast and bilateral axillae were normal in all patients. Radiological diagnosis available in female patients (4) was suggestive of benign breast lesions [Table 2, Figure 1]. Patients were referred for FNAC.

Table 1

Detailed clinical findings

Table 2

Cytological findings, diagnosis and its correlation with radiological and histological diagnosis

Figure 1

Mammogram (Case 1). Left cranio-caudal (left) and medio-lateral oblique (right) mammogram shows solid cystic soft tissue density mass lesion in peri-areolar region

Cytological findings

Case 1–3

FNAC yielded thick pultaceous aspirates. Smears showed many AS and NBSC in a clean background. In addition, few clusters of benign breast epithelial cells and few adipocytes were also seen (Case 2, 3). Although cytological diagnosis was of EICB, considering the age of the patient (Case 1), D/D of fibroadenoma (FA) or fibrocystic disease (FCD) with squamous metaplasia (SM), and metaplastic carcinoma (MCa) were also considered [Figure 2a, b].

Figure 2

Case 1: (a) FNA smear shows many anucleated squames and non-neoplastic mature benign squamous cells (Giemsa, ×300); (b) biopsy shows epidermal inclusion cyst and normal breast tissue (H and E, ×200). Case 4: (c) FNA smear shows anucleated squames in inflammatory background (Giemsa, ×300); (d) lumpectomy specimen showing, epidermal inclusion cyst with mild inflammation and (e) dense inflammation within mammary fat (H and E, ×200)

Case 4

FNAC yielded a purulent aspirate; smears showed features of breast abscess, and repeat FNAC was advised after a course of antibiotics. Patient again presented after a month with 1.5 × 1 cm lump at the same site and a pus-discharging sinus. Repeat FNAC yielded purulent aspirate, and smears showed many AS within acute inflammatory background. No granuloma or atypical cells were seen, thus a diagnosis of infected EICB was given. She again received antibiotics with slight improvement in her symptoms. Lumpectomy was performed to rule out malignancy [Figure 2c–e].

Case 5, 6

Cytomorphological features were similar to those of Case 1–3, thus suggestive of EIC.

Histological findings

Biopsies from Case 1–3 and 5 were diagnosed as EICB, while lumpectomy specimen from Case 4 was diagnosed as infected EICB on histology. Since Case 6 was a young male clinically suspected of gynecomastia with cytological diagnosis of EICB, he refused to undergo any surgery [Figure 2].

Discussion

Breast EIC may arise due to various mechanisms that may result in damage to epidermis which further gets implanted deep within the breast tissue (congenital cyst secondary to obstructed hair follicles/pores, post-trauma, reduction mammoplasty, needle biopsy).[1-3] Other mechanisms include SM of normal columnar cells within an ectatic duct in an area of FCD, FA or phyllodes tumors (PT).[4] In the present study, the mechanism appears to be obstruction of hair follicle, as there was no history of previous trauma, surgery or lump in the breast. Clinically, in general, EIC at other sites occurs as macroscopic firm nodular protrusions from the skin. Breast has flexible fat and mammary gland tissue under its skin, thus EICB grows deep inside the subcutaneous tissue and is difficult to distinguish from a breast tumor. Radiologically on mammography, EICB appears as non-calcified, well-circumscribed lesion, and on ultrasonography (USG) it appears as solid, circumscribed and complex mass.[341415] Thus, even when the mammography of a palpable mass is consistent with a benign lesion, the finding of a solid lesion on USG may need tissue diagnosis to exclude an FA, PT and low-grade malignant breast lesions such as mucinous carcinoma. Denison et al.[15] in their report on cysts extending into the dermis described specific USG features of EICB. An onion ring pattern with alternating concentric hyperechoic and hypoechoic rings has been described corresponding to the multiple layers of lamellated keratin in EICB.[615] Of the five reports on cytological diagnosis of EICB, mammography was done in two cases, and only in one case a D/D of EICB was considered.[10] In the present study, radiological diagnosis was of benign breast lesions.

EIC yields a dirty whitish aspirate, which on smears shows numerous AS or NBSC better seen on Giemsa stain. Due to the intraparenchymal nature of the lesion, sometimes adjacent normal breast epithelial cells and adipocytes can also be included. Since EICB is rare, diagnosis of SM in FA, FCD, PT and rarely MCa, depending upon the age of the patient, is also kept as D/D in such lesions. Lilleng et al.[13] found only one case of EIC out of 779 histologically documented benign breast lesions from surgical biopsies over a period of 10 years. Das et al.[11] reported three cases of EIC/pilar cysts in FNA from 188 males with breast lesions. Only one of the three reports had histological correlation; it indicated a pilomatrixoma. Kapila and Verma[12] were able to detect only five cases of EIC out of 424 benign aspirates from 651 males over a period of 22 years. Histopathological correlation was not available in any of these cases. Although EICB has been reported in males mostly on cytology, the present study shows female preponderance.

In the present study, D/D included carcinoma (Case 1) since the patient was old; FCD (Case 2) due to fluid aspirate and presence of few benign epithelial cells; tuberculous breast abscess (Case 3) due to the purulent aspirate and past history of ATT; and gynecomastia (Case 4). Since smears from all cases showed AS and NBSC, cytological diagnosis was of EICB.

EICB can cause severe complications; potential ones include spontaneous rupture leading to inflammation and abscesses. In Case 4, there was spontaneous rupture of the EIC and the patient presented with a discharging sinus in the peri-areolar region. Although these cysts are benign, they may rarely have malignant transformation into squamous cell carcinoma (SCC). Menville et al.[8] found that 19% of the patients with EIC in their series showed malignant squamous cell lining on histopathology. However, Cameron and Hilsinger[7] reported that malignant transformation of the cyst wall epithelium occurs very rarely (0.045%). Willis[9] and Haselton[16] also reported a possible role of EIC in the origin of SCC of breast. Overall, the incidence of EICB is less; reports are variable on its malignant change, thus actual percentage is uncertain. Malignant change occurs more in the EICB, as compared to EIC at other sites, and it may be due to SM of the mammary duct epithelium. Some authors have reported Paget's disease in the EIC arising from nipple/peri-nipple epidermis.[17]

To conclude, EICB is not a rare entity and can remain under-reported because of its insignificant clinical presentation. Radiologically, it appears as solid mass lesions with well-defined borders, and therefore possibility of well-defined benign or malignant lesion is difficult to exclude. Thus, FNAC plays a significant role in the diagnosis of EICB based on the presence of a typical pultaceous aspirate and cytomorphological features. Asymptomatic lesions can be followed up by imaging; symptomatic ones should be readily excised and need histological correlation to rule out any potential complications that can arise from these cysts.