Primary intracystic squamous cell carcinoma of the breast: A case report and review of the literature.

Primary intracystic squamous cell carcinoma (SCC) of the breast is an extremely rare entity and has a low incidence in comparison with other breast cancers. We report a rare case of primary intracystic SCC in a 45-year-old woman who presented with a cystic lump in the right breast. Cytological smears of the fluid aspirated from the breast tumor revealed malignant squamous cells dispersed in single and occasional groups along with numerous cyst macrophages, suggesting cystic SCC. Histological study of the mastectomy specimen confirmed the diagnosis of primary intracystic SCC. Although the presence of abundant foamy macrophages in the background of fine needle aspiration cytology smears of the breast suggest benign breast lesion, when associated with malignant squamous cells, these suggest cystic primary SCC or metastatic SCC. The primary SCC should not be confused with metaplastic change in other breast carcinomas.

Introduction

Primary intracystic squamous cell carcinoma (SCC) in the breast is an extremely rare neoplasm. Intracystic carcinoma accounts for 0.7% of all breast carcinomas.[1] The origin of this tumor is controversial and the exact histogenesis is still unclear. Primary SCCs in the breast are quite rare, although SCC mixed with ductal carcinoma is more common.[2] It can arise from metaplastic epithelium associated with other primary malignancy of the breast, metastasis from primary elsewhere in the body or an extension of malignancy from the skin covering. We report a case of primary intracystic SCC because of its extreme rarity.

Case Report

A 45-year-old female presented with a lump in the right breast, which she had noticed since three weeks. The lump gradually increased in size. There was no history of discharge from the nipple. Her menstrual cycles were regular and she had two children.

Clinical examination revealed a firm cystic lump of 12 × 10 cm in the upper inner and central quadrant of the right breast. The skin over the right breast appeared stretched, with a slight retraction of the nipple. There was no enlargement of draining lymph nodes. The left breast was normal, without any evidence of a palpable mass. The clinical diagnosis of malignancy of the right breast was made. Pre-operatively, the patient was relegated to clinical stage III (T3N0M0).

Ultrasonographic examination of the right breast showed an irregular-shaped hypoechoic lesion measuring 12 × 6 cm with an internal anechoic area measuring 6 × 3 cm, suggesting a cystic malignant tumor. Routine hematological and biochemical examinations were normal. Fine needle aspiration from the lump in the right breast yielded 10 ml of pale yellow serous fluid. The size of the lump was slightly reduced after aspiration. Wet-fixed and air-dried smears were prepared from the centrifuged aspirated fluid and were stained with Papanicolaou (PAP) stain and May-Grünwald-Giemsa (MGG) stain, respectively.

Cytology

The smears studied were cellular and showed malignant squamous cells predominantly in singles and occasional syncytial groups, and some cells were spindle shaped. The background showed numerous cyst macrophages with little necrosis [Figure 1]. The malignant squamous cells had rounded borders with hyperchromatic enlarged nucleus and coarse irregular granular chromatin. Cytoplasm of the squamous cells showed a variable degree of keratinisation [Figure 2]. A diagnosis of intracystic SCC was made.

Figure 1

Cytology smears showing malignant squamous cells in singles with numerous cyst macrophages (MGG, ×400)

Figure 2

Cytology smear showing malignant squamous cells in singles, demonstrating cytoplasmic keratinisation (PAP, ×400)

To exclude metastatic SCC, a search for remote primary SCC included chest radiograph, cystoscopy, colposcopy, oesophagogastroscopy, laryngoscopy and cervical Pap smear, which did not reveal any extramammary cancer. The criteria required to define a “pure” SCC of the breast were fulfilled. The criteria include: (1) no other neoplastic element, such as ductal or mesenchymal ones, are present in the tumor, (2) the tumor is independent of adjacent cutaneous structures and (3) no other distant epidermoid tumor exists in the patient.[34] Later, simple mastectomy with axillary clearance was performed and the specimen was sent for histological examination. The cut-section of the mastectomy specimen showed a large cystic tumor measuring 8 × 3 cm, containing yellow serous fluid.

Histology

Multiple sections studied showed cystic breast tumor. The cystic cavity was lined by dysplastic squamous epithelium with an infiltrating tumor, showing malignant squamous cells in broad sheets, groups and whorls, with keratin-pearl formation and intercellular bridges. There was no evidence of ductal carcinoma on multiple sections studied. Lymph node sections did not show evidence of tumor. The diagnosis of keratinising intracystic SCC was given. Immunostaining for estrogen/progesterone receptor and HER-2/Neu oncoprotein were negative and that for cytokeratin was positive.

Discussion

Pure SCC and adenosquamous carcinoma have been listed under metaplastic breast carcinomas in the World Health Organization classification.[5] The Japanese Breast Cancer Society has defined “SCC of the breast as a special type of cancer, in which malignant cells are arranged in broad sheets and whorls with keratin formation or intercellular bridge”.[6] The incidence of SCC reported in the western countries is 0.1–3.6% and in Japan, it is 0.17%.[6] The age group affected is between 32 and 65 years,[67] with an increased tendency of left-sided involvement. The characteristics of SCC of the breast generally reported are a large-sized tumor, rapidly growing with a central cyst formed by necrosis. These findings are presumably caused by rapid growth of the tumor.[6] This is unlikely in our case because there was little necrosis elsewhere in the tumor. There are several theories about the origin of SCC of the breast. The possible mode of origin of SCC is epidermoid cyst of the breast, chronic abscess and complete metaplasia of glandular breast tissue.[47] Lymph node involvement is reported to be less frequent than might be expected, given the larger tumor size.[6] Indeed, no lymph node was involved in our case. The tumor cells are negative for vimentin, estrogen and progesterone and are diffusely positive for high molecular weight cytokeratin and C-erbB-2.

Squamous cells in fine needle aspiration cytology (FNAC) of breast lesions can be found in various benign lesions, like epidermoid cyst, subareolar abscess, fibroadenoma, infracted papillomas, spindle cell metaplasia, cystic sarcoma phyllodes, pseudosarcoma and malignant breast tumors or metastatic malignancy.[78] The benign breast conditions with abundant squamous cells may sometimes mimic malignant squamous lesion and vice versa. In general, the presence of abundant foamy macrophages in the background suggests a benign lesion. Benign squamous cells are bland looking and are often associated with anucleated squames, and no tumor, cell cannibalism. The malignant squamous cells are more pleomorphic, mitotically active and dyskeratotic and, sometimes, bizarre-shaped cells can be seen.[9] The differential diagnosis of malignant squamous cells in FNAC of the breast includes primary SCC and metastatic SCC of the breast.[4] Careful assessment of cytological features of squamous cells and the background appearance appears to be critical for arriving at a correct diagnosis. However, in the case of intracystic SCC, numerous foamy macrophages coexist with malignant squamous cells.

The clinical behavior of this tumor is uncertain. Hormonal therapy is not indicated as most cases of SCC are negative for hormonal receptors. SCC of the breast is reported to be resistant to both radiotherapy and standard chemotherapy performed for invasive ductal carcinoma.[9] In our case, radical mastectomy with axillary clearance was performed with postoperative adjuvant therapy, as given for common types of breast cancers. There was no evidence of recurrence of the tumor after four years of treatment.

In conclusion, the presence of malignant squamous cells in fine needle aspiration of the breast suggests primary SCC or metastatic SCC. The finding of a pure SCC necessitates more accurate work-up to exclude skin lesion or metastasis. The primary SCC should not be confused with a much more largely manifested metaplastic change in other usual breast cancers. Although the presence of numerous cyst macrophages in the background of breast FNAC smears suggests a benign lesion, when present with malignant squamous cells, they suggest intracystic SCC.