Breast mass in a 55-year-old woman

A 55-year-old white woman presented with a one-month history of a palpable breast mass. A mammogram was performed six months prior to her presentation and was read negative. However, the mammogram done two weeks prior to her clinical visit was suspicious for malignancy. Physical examination revealed a 1.5 cm to 2 cm palpable right breast mass. She underwent excision of the mass. Gross examination of the mass revealed a 2.5 cm well defined, ovoid-shaped, firm tan white tumor with a scalloped border, irregular extension into the surrounding tissue, and a granular cut surface. Largest tumor diameter was 2.5 cm. Microscopic examination of the tumor revealed small tumor cells with a solid, alveolar, and classic "single file" arrangement. There is also focal expansion and filling of the acini by similar small cells.