Low-grade adenosquamous carcinoma of the breast with diverse expression patterns of myoepithelial cell markers on immunohistochemistry: a case study

Abstract

This paper reports a case of low-grade adenosquamous carcinoma (LGASC) arising in a 69-year-old woman, who presented with a 1-cm palpable mass on her right breast. Core needle biopsy diagnosed the mass as a fibroadenoma. After six months, the mass increased in size, and the patient received subsequent mammotome excision. On microscopic examination, bland-looking small glands were infiltrating into the fibrotic stroma with lymphocytic infiltrates at the periphery. Hematoxylin and eosin staining revealed relatively easily detectable myoepithelial cells along the outside in each of the glandular structures with variable degrees of squamous metaplasia. Based on histologic features, the patient was diagnosed with LGASC. LGASC is a rare variant of metaplastic carcinoma, which is characterized by a favorable prognosis. Due to the bland cytology and presence of myoepithelial cells, LGASC can be misdiagnosed as benign lesion. Additionally, inconsistent expression of myoepithelial markers could aid the diagnosis of LGASC.

Keywords: Breast; Carcinoma; Carcinoma, adenosquamous.

Fig. 1

Patient's mammography and histologic features of tumor. (A) In initial mammography, nodular density on right lower central of breast parenchyma is observed. (B) At lower magnification, ill-defined lesion is surrounded by peripheral lymphoid infiltration. (C) At high power, angulated or rounded bland-looking glandular structures infiltrate into desmoplastic fibrous stroma. Myoepithelial cells are easily detected at the outside of glandular structures. (D) Variable degree of squamous metaplasia found in glandular lumens.

Fig. 2

p63 (A) and actin (smooth muscle actin) (C, D) are expressed in over 90% of myoepithelial cells. (B) Some tumor epithelial cells are expressing p63, whereas some myoepithelial cells are not expressing p63. Some areas of the tumor myoepithelial cells show relatively consistent expression of myoepithelial cell markers (E, CD10; G, S-100 protein; I, smooth muscle myosin heavy chain [SMMHC]; K, caldesmon), whereas other areas show less or no expression of myoepithelial cell markers (F, CD10; H, S-100 protein; J, SMMHC; L, caldesmon) compared to normal mammary glands (insets).