Pseudoangiomatous hyperplasia of the mammary stroma: true entity or phenotype?

We report the clinical and pathologic features seen in 14 cases of pseudoangiomatous hyperplasia of the mammary stroma. The lesion manifested as a discrete palpable lump in twelve women and two men. The excisional biopsy specimens showed firm, circumscribed grey-tan lesions measuring from 3 to 5.5 cm in largest dimension. Histologic study revealed diffuse, anastomosing, enlongated slits with open lumina, covered by spindle cells with bland nuclei and no mitotic activity. Strong reactivity for vimentin and CD34 was noted. Smooth muscle actin was focally noted in most cases. Immunostains for other markers, including CD31 and factor VIII related antigen was negative. Spindle cells from two cases expressed both estrogen and progesterone receptors. In all the cases, there was some degree of glandular hyperplasia accompanying the stromal changes. Fibroadenoma or fibrocystic disease were also common features. Our study confirms that pseudoangiomatous hyperplasia of mammary stroma represents a proliferation of local myofibroblasts, likely related to a hormonal stimulus. The wide range of associated changes of breast parenchyma further indicates that this lesion may represent a local, non specific change rather than a true clinico-pathologic entity.