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.

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