Nodular myofibroblastic stromal hyperplasia of the mammary gland as an accurate name for pseudoangiomatous stromal hyperplasia of the mammary gland.

Pseudoangiomatous stromal hyperplasia (PASH) of the mammary gland is a well-known benign localized form of stromal overgrowth with probable hormonal etiology. We describe the histologic findings and immunohistochemistry of two cases. Two women, 16 and 58 years old, presented with a breast mass and underwent surgical excision. Grossly, they consisted of a well-circumscribed, rubbery tissue with a solid white-tan homogeneous cut surface. One of the cases showed focal cystic areas. Histologically the lesion showed a proliferation of the collagenous stroma with varying degrees of density, and hyalinization with many pseudovascular slit-like anastomosing spaces lined by spindle cells with scant cytoplasm and bland chromatin. The spindle cells lining the spaces were strongly reactive for vimentin and weakly reactive for CD34, actin, and desmin. They were negative for factor VIII, S-100, and pankeratin. In PASH, the "pseudoangiomatous" term describes a recognizable pattern but does not describe the tumor's histologic nature. We propose the name nodular myofibroblastic hyperplasia of the mammary stroma as a more accurate name.