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pseudoangiomatous stromal hyperplasia

Sunday 2 April 2017


Definition: Pseudoangiomatous stromal hyperplasia / PASH shows a myofibroblastic proliferation that stains positive for SMA and vimentin. The spindle cells may show CD34 reactivity.


- Pseudoangiomatous stromal hyperplasia - PASH

Breast pseudo-angiomatous stromal hyperplasia typically occurs in premenopausal women, but is not altogether uncommon in men, and is frequently found incidentally during biopsy for suspected gynecomastia.

The condition may present clinically as a firm but painless breast mass. If pseudo-angiomatous stromal hyperplasia develops during pregnancy, it may cause massive breast enlargement, and skin necrosis.

Around 30% of PASH lesions are discovered as a palpable mass, with the other 70% detected radiologically, or as an incidental finding while looking for something else on biopsy. Patients usually describe a palpable PASH mass as mobile, firm, and painless.

The average age of development of pseudo-angiomatous stromal hyperplasia of the breast is about 50, but there is quite a bit of variability. PASH of the breast is usually described in females within the ‘child bearing‘ age group, but has been noted in children as young as 12, and in women in their early 70s.

Pseudoangiomatous stromal hyperplasia is considered a ‘mesenchymal‘ lesion (formed from genetically immature muscle and connective tissue cells), and is composed mostly of myofibroblasts, but also sometimes includes glandular components.

The cause of pseudo-angiomatous breast hyperplasia is unknown, but it is suspected that the ‘aberrant reactivity‘ of myofibroblasts to endogenous or exogenous hormones, and in particular the sex hormones, might be an important contributing factor.

Pseudo-angiomatous breast hyperplasia may occur alone, or along with other proliferative and non-proliferative breast changes. PASH is found as an incidental finding with other benign breast fibrocystic changes at a rate of about 23%.



See also

- mammary anomalies


- Pseudoangiomatous stromal hyperplasia (PASH). A mammary stromal tumor with myofibroblastic differentiation. Powell CM, Cranor ML, Rosen PP. Am J Surg Pathol. 1995 Mar;19(3):270-7. PMID: 7872425