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

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. Sometimes cells were nested grouped and similarly surrounded by thick collagen bands. Cells had round to spindle-shaped nuclei with one or two visible nucleoli. 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 alpha-smooth-muscle actin and focal staining to desmin, CD34, and bcl-2 protein. This immunophenotype, similar to what is observed in breast myofibroblastoma, is consistent with the fibro/myofibroblastic differentiation of stromal cells. 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.