Mammary-type myofibroblastoma | |
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Other names | Mammary and extramammary myofibroblastoma |
Micrograph of mammary myofibroblastoma. H&E stain. | |
Specialty | Oncology, Pathology |
Mammary-type myofibroblastoma (MFB),[1] also named mammary and extramammary myofibroblastoma,[2] was first termed myofibrolastoma of the breast,[3] or, more simply, either mammary myofibroblastoma (MMFB) or just myofibroblastoma.[4][5] The change in this terminology occurred because the initial 1987 study[3] and many subsequent studies[1] found this tumor only in breast tissue. However, a 2001 study[6] followed by numerous reports[1] found tumors with the microscopic histopathology and other key features of mammary MFB in a wide range of organs and tissues.[1] Further complicating the issue, early studies on MFB classified it as one of various types of spindle cell tumors that, except for MFB, were ill-defined. These other tumors, which have often been named interchangeably in different reports, are: myelofibroblastoma, benign spindle cell tumor, fibroma, spindle cell lipoma, myogenic stromal tumor, and solitary stromal tumor. Finally, studies suggest that spindle cell lipoma and cellular angiofibroma are variants of MFB.[5][7] Here, the latter two tumors are tentatively classified as MFB variants but otherwise MFB is described as it is more strictly defined in most recent publications.[1] The World Health Organization in 2020 classified mammary type myofibroblastoma tumors and myofibroblastoma tumors (i.e. extramammary myofibroblastic tumors) as separate tumor forms within the category of fibroblastic and myofibroblastic tumors.[8]
Mammary MFB likely represents less than 1% of all breast tumors.[9] Extramammary MFB, however, has in recent studies been found to occur far more frequently than mammary MFB: a study of 143 patients reported that extramammary MFB outnumbered mammary MFB 10 to 1.[5] Hence, the overall disease may be more common than previously considered. Extramammary MFB occurs about equally in males and females of both sexes and has a broad age distribution that includes children. Mammary MFB likewise occurs about equally in both sexes but has a decided predominance in middle-aged and older adults.[9]
MFB are completely benign tumors, i.e. they do not metastasize and when surgically removed rarely recur.[1] Microscopically, they consist of neoplastic spindle cells,[10] i.e. cells that are longer than wide, have a morphology somewhere between fibroblasts and myofibroblasts, have similarly appearing counterparts in normal tissues, and in normal tissues are usually identified as fibroblasts.[9] The neoplastic cells commonly: 1) have acquired a gene chromosome abnormality in which a small part of chromosome 13 is deleted;[9] 2) fail to express the retinoblastoma protein (pRb) due to this deletion;[11] and 3) contain key tumor marker proteins.[9] A tumor with this characteristic microscopic appearance, 13q14 deletion, loss of pRb, and presence of marker proteins strongly indicate that it is a MFB[7] and, importantly, distinguishes it from other more aggressive tumors that it may otherwise resemble and be diagnosed as.[12]