PASH is a benign proliferation of the mammary stromal tissue. On histologic analysis, it shows complex interanastomosing slit-like spaces which appear to be lined by spindle cells in the breast parenchyma.
It is important to differentiate the lesion from angiosarcoma. It can be confused histologically with PASH. Angiosarcoma often shows a more aggressive infiltrative pattern into surrounding fibroadipose breast tissue and is highly vascular, lined by endothelial cells. It does not show a collagenous stroma. Angiosarcoma displays positive immunoreactivity for CD31 and, although less frequently and with less sensitivity, for the factor VIII–related or von Willebrand factor antigens.
PASH is associated with several benign entities including proliferative and nonproliferative fibrocystic changes, such as fibroadenomas, gynecomastia, normal breast tissue, and sclerosing lobular hyperplasias. The etiology and pathogenesis remain unknown.
Local excision is curative in most cases. Although recurrence may occur, the overall rate is low. Follow-up after excision is recommended as local recurrence has been reported.