Myxoid Myofibroblastoma of the Breast With Atypical Cells

The differential diagnosis of myxoid lesions in the breast is broad and includes both benign and malignant entities. Assessment is particularly challenging on core biopsy specimens. Myofibroblastoma, initially thought to be more common in the adult male breast, is being recognized with increasing frequency in the female breast. The wider anatomic distribution of mammary-type myofibroblastoma has also become known, and many new morphological variants have been described. Though focal myxoid stroma may be noted in myofibroblastomas and occasional myofibroblastomas may contain atypical cells, there have been only 3 reports in the literature of myofibroblastomas with exclusive or predominantly myxoid stroma, and 2 of these contained atypical cells. We report another case of mammary myxoid myofibroblastoma with atypical cells in a 40-year-old woman and discuss the differential diagnoses of myxoid lesions in the breast.