Deciduoid-like myofibroblastoma of the breast: a potential pitfall of malignancy

Recently, we have encountered a case of mammary myofibroblastoma (MFB) composed exclusively of deciduoid-like cells similar to those previously reported by us in non-neoplastic conditions. We think that the tumour presented here is a previously unrecognized morphological variant of MFB, for which the descriptive term ‘deciduoid-like MFB’ is proposed. This case appears unique in that, being composed exclusively of deciduoid-like cells, it was difficult to recognize as MFB. The differential diagnosis included both malignant and benign tumours, such as apocrine carcinoma, melanoma, pleomorphic rhabdomyosarcoma, epithelioid leiomyoma, epithelioid angiomyolipoma and epithelioid schwannoma