Exuberant Smooth Muscle Cells in Fibroadenoma of the Breast: A Case Report

ABSTRACT

Smooth muscle cell metaplasia is an extremely rare form of stromal differentiation in fibroadenomas. We describe a case of fibroadenoma with exuberant smooth muscle cells in a 72-year-old woman. The mass was located in the upper central portion of the left breast. It was well circumscribed and its greatest dimension was 3 cm. Histologically, the glandular elements resembled the appearance of fibroadenoma, but the stromal elements were composed of spindle cell bundles with abundant eosinophilic cytoplasm and elongated cigar-shaped nuclei. Neither mitotic activity nor cellular atypia was seen. The stromal cells were immunohistochemically positive for smooth muscle actin, calponin, desmin, and estrogen receptor-beta, but negative for CD34, S-100 protein, p63, CD10, estrogen receptor-alpha, progesterone receptor and cytokeratin. These results proved that the stromal cells showed features of smooth muscle cells.