DIAGNOSIS: Epithelioid myofibroblastoma
DISCUSSION: Myofibrobastoma is a benign lesion that is part of the spectrum of spindle cell lipoma. The lesion is composed of myofibroblasts, which may range from spindle cells resembling a schwannoma, to epithelioid cells which mimic a carcinoma. The epithelioid variant may be mistaken for an invasive lobular carcinoma, and the expression of estrogen receptor by myofibroblastoma can be further confusing. However, lack of cytokeratin expression excludes carcinoma. Myofibroblastomas characteristically express CD34 and usually express desmin and smooth muscle actin.