Myxoid Fibroadenoma of the Breast With Radiologic-Pathologic Correlation: A Case Report.

Myxoid fibroadenoma is a rare histologic variant of conventional fibroadenoma characterized by prominent hypocellular myxoid stromal change. Owing to its overlapping morphologic features with other myxoid breast lesions, including mucinous carcinoma and phyllodes tumor, it may pose a significant diagnostic challenge, particularly in limited biopsy specimens. We report the case of a 47-year-old woman presenting with a non-palpable breast mass, initially evaluated with imaging and core needle biopsy. Preoperative histopathologic assessment demonstrated a fibroepithelial lesion; however, definitive diagnosis remained uncertain because of the prominent myxoid stromal component and limited sampling. Surgical excision was therefore performed, and complete histopathologic examination established the diagnosis of myxoid fibroadenoma. Microscopic evaluation revealed a well-circumscribed benign biphasic fibroepithelial lesion composed of epithelial and stromal components with abundant hypocellular myxoid stroma, without cytologic atypia, stromal overgrowth, or increased mitotic activity. Myxoid fibroadenoma is an uncommon benign breast lesion that may mimic malignant or borderline breast neoplasms, particularly in limited biopsy specimens. Awareness of this rare entity and careful radiologic-pathologic correlation are essential to avoid misdiagnosis as an aberration of the normal development and involution (ANDI).