Lipomatous myofibroblastoma: a potential diagnostic pitfall in the spectrum of the spindle cell lesions of the breast

Abstract

We report on two cases of myofibroblastoma (MFB) of the breast comprised predominantly of a mature fatty component, representing approximately three quarters of the entire tumour area. Both tumours consisted of a well-circumscribed lipomatous tumour mass containing dispersed nodular or irregularly shaped spindled cellular areas. The fatty component was represented exclusively by mature adipocytes, uniform in size and shape, lacking nuclear pleomorphism. The cellular areas contained spindly to oval cells with morphological and immunophenotypical features typical of MFB. The two components were so intimately admixed that a finger-like infiltrating growth pattern was apparent. The cases reported here as "lipomatous MFB" aim to clarify further the morphological spectrum of MFB of the breast. Lipomatous MFB may potentially mimic other benign or aggressive tumour-like lesions or even bland-looking malignant spindle cell tumours such as fibromatosis, nodular fasciitis, spindle cell lipoma, spindle cell liposarcoma, spindle cell variant of metaplastic carcinoma, spindle cell malignant myoepithelioma, and low-grade fibrosarcoma/malignant fibrous histiocytoma. The histogenesis of the present bimorphic mesenchymal tumours could be explained as the result of a dual, myofibroblastic and lipomatous, differentiation from a common pluripotential mesenchymal precursor cell, probably represented by the vimentin+/CD34+ fibroblast of the mammary stroma.

CD34 + fibrocytes in tubular carcinomas and radial scars of the breast

“…Tubular carcinomas disclosed a complete loss of stromal CD34 + fibrocytes accompanied by a gain of stromal a-SMA expression. However, the presence of stromal CD34 + fibrocytes is, as shown in the present and other studies, a feature of benign breast lesions [3,7,11,12,13,14,18]. In this context, radial scars appear to merit special attention, as these lesions are the first benign mammary lesions reported to disclose a partial loss of CD34 + fibrocytes.…”

“…The normal mammary stroma as well as mesenchymal tumors of the breast, such as benign spindle cell stromal tumors [11,12,13], phyllodes tumor and fibroadenoma [14,18], harbor huge numbers of CD34 + fibrocytes. To date, the histogenesis and function of this cell type is a matter of speculation and remains to be clarified [5,6].…”

Fibromatosis of the breast parenchyma with a benign-like nodular appearance

“…The former is a benign tumour arising in the mammary stroma, which can be confused with fibromatosis in that it is composed of spindle-shaped cells arranged in short intersecting fascicles interrupted by keloidal-like collagen bands 20,21 . In myofibroblastomas that contain a significant intratumoural fatty component (lipomatous myofibroblastoma), the spindleshaped cells, closely intermingling with adipocytes, impart a fibromatosis-like infiltrative pattern to the tumour 22 . Unlike myofibroblastoma, fibromatosis exhibits infiltrative, at least focally, margins, entraps fat and glandular breast tissue, and the neoplastic cells lack diffuse expression of desmin, CD34, oestrogen/ progesterone receptors and bcl-2 protein [20][21][22][23] .…”

“…In myofibroblastomas that contain a significant intratumoural fatty component (lipomatous myofibroblastoma), the spindleshaped cells, closely intermingling with adipocytes, impart a fibromatosis-like infiltrative pattern to the tumour 22 . Unlike myofibroblastoma, fibromatosis exhibits infiltrative, at least focally, margins, entraps fat and glandular breast tissue, and the neoplastic cells lack diffuse expression of desmin, CD34, oestrogen/ progesterone receptors and bcl-2 protein [20][21][22][23] . Inflammatory myofibroblastic pseudotumour is a fibroinflammatory lesion which can be rarely encountered in the breast parenchyma 24 .…”

Myxoid myofibroblastoma of the breast with atypical cells: a potential diagnostic pitfall

“…Differential diagnosis mainly revolved around the myxoid type of spindle cell lipoma and solitary fibrous tumour. Discrimination between myofibroblastoma and spindle cell lipoma/ solitary fibrous tumour may be difficult, as they are closely related neoplasms, likely arising from a common mammary stromal stem cell capable to differentiate along several [4][5][6]. This hypothesis is supported by the fact that all these tumours share some morphological and immunohistochemical features and by the recognition of hybrid tumours that simultaneously exhibit features of MFB and solitary fibrous tumour or MFB and spindle cell/pleomorphic lipoma [3,5,6].…”