Abstract
Myofibroblastoma (MFB) of the breast is a rare benign mesenchymal tumor originating from mammary stromal cells, posing diagnostic challenges due to its diverse presentation. It typically affects older individuals, often postmenopausal women and men aged 40-87 years, presenting as a solitary, painless, well-defined, mobile mass that grows slowly. On mammography, MFB typically manifests as a well-circumscribed, non-calcified, round or oval mass, often of equal or high density, though margins can sometimes be obscured or indistinct, and rare coarse calcifications have been reported. Ultrasound findings are variable but often demonstrate a solid, irregular, non-circumscribed mass with varying posterior acoustic features and vascularity. Diagnosing MFB requires core needle biopsy and immunohistochemistry, as imaging findings are non-specific. However, MFB encompasses a broad morphologic spectrum beyond the classic spindle cell type and sometimes demonstrate mixed variants that can exhibit unusual or alarming features that make diagnosis challenging. A key feature is the presence of interspersed thick, hyalinized, and eosinophilic collagen bundles. Immunohistochemically, MFB characteristically shows strong positivity for CD34 and desmin. Treatment involves surgical excision, which is curative, and the prognosis is excellent with an extremely low risk of recurrence and no metastatic potential. Accurate differentiation from malignant mimics, particularly invasive lobular carcinoma and metaplastic carcinoma, is crucial. This case report describes a 41-year-old female who was found to have a suspicious right breast mass on a diagnostic ultrasound, later confirmed as MFB through pathology. Given the rarity of MFB, this case underscores the importance of accurate diagnosis and a multidisciplinary approach involving radiology, pathology, and surgery for appropriate management.