Abstract
Background: We report here a case of mammary myofibroblastoma, a rare benign mesenchymal tumor.
Case: A 75-year-old woman reported a gradually growing mass in the right breast, and visited Osaka University Medical Hospital. It was clinically diagnosed as a borderline phyllodes tumor. Aspiration biopsy cytology showed spindle or ovoid tumor cells were present solitarily or fascicularly. Different-sized vacuoles suggestive of adipose tissue and light-green-stained band-like material suggestive of collagen fiber were admixed. No epithelial component was observed. The cytologic diagnosis at the time was a borderline phyllodes tumor. Histological examination of mastectomy specimens showed the tumor to be composed of spindleshaped cells with eosinophilic cytoplasm with scattered fat globules, hyalinized collagenous bands, and myxoid material present. Although relatively high mitotic activity was observed in some areas, nuclear atypia was mild. Immunohistochemistry showed that tumor cells were strongly positive for vimentin and a-smooth muscle actin. MIB-1 staining showed approximately 20 positive cells per 100 tumor cells in some areas. The histologic diagnosis of the tumor was myofibroblastoma of the mammary gland.
Conclusion: Myofibroblastoma is a tumor difficult to diagnose with certainty by cytology, but it is important to consider the possibility when fat cells are admixed with spindle-shaped tumor cells.
