Mammary myofibroblastoma: a clinico- pathologic study of six cases

Mammary myofibroblastoma is a rare and benign neoplasm of the breast stroma, showing features of fibroblasts and myofibroblasts. It has also been noted to exhibit smooth muscle cell characteristics.

The aim of this study was to describe the clinical and pathological features of mammary myofibroblastoma reported at our institution.

Cases of mammary myofibroblastoma reported in our laboratory were retrieved by electronic search. H&E slides were reviewed and clinico-pathologic features were noted. Immunohistochemistery was performed by Envision method. Only CD34 and CKAE1/AE3 were performed in all 6 cases. ASMA, desmin and S-100 were performed in 5, 4 and 2 cases, respectively. Vimentin and Bcl-2 were performed in one case.

A total of 6 cases were identified. Five were female and one was male. The mean age of patients was 45.5 years. The mean size of tumors was 7.7 cm in the largest dimension. Histologically, four cases showed clusters of uniform bipolar spindle shaped cells separated by broad bands of hyalinized collagen. Mitotic figures ranged from none to 3 mitoses/10 HPFs. One case showed combined features of cellular and fibrous areas. Another case was epithelioid-cell type. On immunohistochemistry, CD34 stain was positive in 5/6 cases, ASMA in 3/5 cases, desmin in 2/4 cases, S-100 in none and vimentin and Bcl-2 in 1/6 cases. None of the cases stained positive for CKAE1/AE3.

Due to the varying degree of fibro-myofibroblastic differentiation, myofibroblastoma shows multiple morphologies and several intratumoral and intertumoral types. It is essential to distinguish each variant from the other to avoid inaccurate diagnosis of other benign or malignant breast conditions, becoming a noteworthy diagnostic dilemma for histopathologists.