Pseudoangiomatous stromal hyperplasia of the breast.

Pseudoangiomatous stromal hyperplasia is a relatively common lesion of the breast. In general, it is less commonly found as a clinically palpable mass and is more commonly found as incidental microscopic foci. It is a benign proliferative, probably neoplastic, hormonally driven process of the mammary stromal myofibroblasts. The clinical, radiologic, and cytologic findings can resemble those of fibroadenoma. Histologically, it can be confused with low-grade angiosarcoma. The exact etiology of pseudoangiomatous stromal hyperplasia is still controversial, but a neoplastic process of the stromal myofibroblasts, with a hormonal stimulus in its development and progression, is the favored theory. Most lesions can be cured by complete surgical excision, and patients undergoing the excision have a good prognosis.