Myofibroblastoma-like changes in fibro(stromo)-epithelial lesions of the breast: report of two cases

Abstract

Sir, Apart from the well-known epithelial/stromal tumors of the breast, such as fibroadenoma and phylloides tumors, another group of biphasic lesions, showing a wide morphological spectrum on a common basic theme, does exist. These lesions have been variably termed “fibroepithelial tumors,” “hamartomas,” “fibroadenoma variants,” and “stromo-epithelial lesions” [1, 2, 3, 6]. The epithelial component usually features florid/sclerosing adenosis and ductal epithelial hyperplasia. The stromal component is usually composed of fibrous tissue in which mature lipomatous or cartilaginous or osseous components (hamartoma) may be occasionally encountered [6]. Although there is the possibility that stroma may also display a variable fibro/myofibroblastic and myoid differentiation [2, 3], to the best of our knowledge, myofibroblastomalike changes have not been reported in mammary fibroepithelial (hamartomas) lesions. Two women (25 years and 49 years) presented with two nodular breast masses, measuring 1.5 cm and 2 cm in greatest dimension, respectively, which were surgically excised with the pre-operative diagnosis of fibro-adenoma. Histologically, both surgical samples showed the typical features of the so-called “fibro-epithelial lesion,” being composed of an admixture of glandular and stromal component proliferation. The epithelial component consisted of florid and sclerosing adenosis admixed with foci of typical ductal hyperplasia. In both cases, the stroma was completely replaced by bland-looking oval to spindle cells with pale to slightly eosinophilic cytoplasm, arranged in short irregularly intersecting fascicles, interrupted by thick bands of brightly eosinophilic collagen (Fig. 1A, B). Sometimes cells were nested grouped and similarly surrounded by thick collagen bands (Fig. 1C). Cells had round to spindle-shaped nuclei with one or two visible nucleoli (Fig. 1B). These stromal changes were closely reminiscent of myofibroblastoma, typical type, of the breast. Immunohistochemically, the cells of both cases had a similar profile: diffuse and strong immunoreactivity to vimentin and a-smooth-muscle actin (Fig. 1D) and focal staining to desmin, CD34, and bcl-2 protein. No staining was obtained for calponin, h-caldesmon, and S100 protein. This immunophenotype, similar to what is observed in breast myofibroblastoma, is consistent with the fibro/myofibroblastic differentiation of stromal cells. It is well known that mammary stroma has the capability of modulating its cellular phenotype as well as its extracellular matrix components upon several pathological conditions. As tumors of mammary stroma (fibroadenoma, myofibroblastoma, solitary fibrous tumor, leiomyoma), fibro(stromo)-epithelial lesions are examples in which presumptive fibroblast-like mammary stromal stem cells may undergo multidirectional mesenchymal differentiation [4, 5]. This event may well explain the occurrence of a stromal fibromatosis-like fibro/myofibroblastic and/or myoid (leiomyomatous) differentiation in these lesions [2, 3]. The present study provides evidence that mammary stromal cells in fibro-epithelial lesions may also acquire morphological and immunohistochemical features similar to those observed in myofibroblastoma, supporting the hypothesis that such cells (interlobular? and/or intralobular?) are the precursors of myofibroblastoma. Similar myofibroblastoma-like stromal changes have been reported in the more cellular areas of “pseudoangiomatous stromal hyperplasia,” a lesion which is thought to be histogentically related to myofibroblastoma [7]. Although the characteristic slit-like spaces of this lesion are lacking in our cases, the possibility that we are dealing with a nodular, cellular variant of pseudoangiomatous stromal hyperplasia cannot be completely ruled out. G. Magro ()) Dipartimento G.F. Ingrassia, Anatomia Patologica, Universit di Catania, 95123 Catania, Italia e-mail: g.magro@unict.it Tel.: +39-95-3782024 Fax: +39-95-3782023