Mammary myofibroblastoma with leiomyomatous differentiation: case report and literature review

Introduction. Myofibroblastoma of the breast (MFB) is an unusual benign tumour that belongs to the family of benign spindle cell tumours of the mammary stroma. The detection of smooth muscle cells in MFB is explained by its histogenesis from CD34+ fibroblasts of mammary stroma capable of multidirectional mesenchymal differentiation, including smooth muscle. Aims. The purpose of this case is to highlight characteristics of this rare neoplasm. Immunohistochemical features, in MFB with predominant leiomyomatous differentiation, are provided to offer a practical approach to a correct diagnosis. Case report. We report a right MFB in a 60-year-old male. The tumour was unusual due to its morphological features, with predominant leiomyomatous differentiation. Immunohistochemical findings, based on the negativity of h-caldesmon, helped in reaching a diagnosis. Conclusion. The detection of leiomyomatous rather than myofibrolastic features in MFB may reflect only the predominant cell types of examined area, and this is not necessarily representative of the remaining tumour which may have a different basic cellular composition. Immunohistochemical expression of h-caldesmon is a reliable marker in distinguishing smooth muscle versus myofibrolastic cellular differentiation in spindle cells lesions of the breast.