Myofibroblastoma (MFB) is a rare mesenchymal tumor arising in breast's soft tissue with a great variety of microscopic features that can be mistaken with a wide variety of biphasic lesions. The authors report a rare case of myofibroblastoma of the breast arising in a mammary hamartoma (MH), present a review of the clinicopathological features of these lesions, and make some diagnostic considerations. The tumour consisted of a well-circumscribed nodule. MFB component comprised about fifty percent of the lesion and was made up of bipolar spindle cells arranged in fascicular clusters separated by bands of hyalinized collagen. There were fat cells and several residual hamartoma glands intermingled and distorted in MFB area. MFB component was positive for Desmin, CD34, bcl-2, and Calponin. To the best of our knowledge, MFB has not been reported in MH, neither has any of the reports described mammary glands joined within MFB. 1. Introduction Myofibroblastoma (MFB) is a rare mesenchymal tumor arising in breast’s soft tissue [1, 2]. In 1987, Wargotz et al. [2] described a benign tumour of the breast composed of spindle cells arranged in fascicular clusters with interspersed bands of hyalinized collagen and called this lesion “myofibroblastoma”. After that, several cases have subsequently been reported, and it has become clear that MFB of the breast may exhibit a greater variety of morphological features than originally described. Glandular structures have not been described in MFB [3–9]. Mammary hamartomas (MH) comprise about 0.7% of all benign breast masses that were first described in 1928 by Prym [10], who referred to them as “mastomas”. Further cases were reported as adenolipomas and fibroadenolipomas. In 1971, Arrigoni was the first to introduce the term mammary hamartoma, that is further characterized by the variety of mature tissues they contain [11]. The authors report a case of MFB developed in MH. This very rare association may be a potential diagnostic pitfall in the spectrum of biphasic cell lesions of the breast. To our knowledge, the coexistence of MFB and MH in the same mass has not been published. 2. Case Report A 59-year-old woman presented with a solitary nodule in the left breast which was first noted on routine mammography. Left breast echography showed a sharply demarcated nodule in the breast parenchyma. A complete surgical excision of the mass was performed. Gross pathology showed a well-circumscribed, round to slightly lobulated, tan, rubbery, 2,5？cm nodule. On cut sections, a whitish tumour mass with scanty interspersed yellow areas was
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