Pseudoangiomatous stromal hyperplasia: an overview.

Pseudoangiomatous stromal hyperplasia (PASH) of the breast is a benign, proliferative mesenchymal lesion with possible hormonal etiology. It typically affects women in the reproductive age group. Pseudoangiomatous stromal hyperplasia is frequently an incidental histologic finding in breast biopsies performed for other benign or malignant lesions. Rarely, it can present as a firm, painless breast mass, which has been referred to as nodular or tumorous PASH. Grossly, tumorous PASH is a well-circumscribed, firm, rubbery mass with solid, homogenous, gray-white cut surface. On histologic examination, it is characterized by the presence of open slitlike spaces in dense collagenous stroma. The spaces are lined by a discontinuous layer of flat, spindle-shaped myofibroblasts with bland nuclei. The spindle cells express progesterone receptors and are positive for vimentin, actin, and CD34. The most important differential diagnosis on histopathology is angiosarcoma. Pseudoangiomatous stromal hyperplasia discovered incidentally does not require any additional specific treatment. Tumorous PASH is treated by local surgical excision with clear margins and the prognosis is excellent, with minimal risk of recurrence after adequate surgical excision.