Aspiration cytology of the collagenized variant of mammary myofibroblastoma: a case report with review of the literature

Myofibroblastoma of the breast is a rare benign stromal neoplasm, which occurs primarily in men. Classical myofibroblastoma is a circumscribed, nonencapsulated tumor comprised of bipolar fusiform cells arranged randomly, or in fascicles alternating with broad collagenous bands. Additional histologic variants (the cellular, collagenized, infiltrative, and epitheloid types) have been described. Several case reports describe the cytopathologic features of the classical and cellular variants. We report on a 70-yr-old woman, who presented with a circumscribed mass in her left breast. Aspiration biopsy showed paucicellular smears with singly distributed atypical spindle-shaped cells and rare fragments of collagenized stroma, raising suspicion of a phyllodes tumor. Histologic examination revealed spindle-shaped cells distributed in a diffusely collagenized stroma. Some nuclear atypia was present. To the best of our knowledge, this is the first case reporting the cytologic features of the collagenized variant of myofibroblastoma. Although we believe a specific diagnosis of myofibroblastoma can be rendered in a male based on the typical cytologic and clinical findings in the classical type, the variant forms are difficult to classify accurately and require excision for a definitive diagnosis.