What is pash?

What is PASH?

PASH (Pseudoangiomatous Stromal Hyperplasia) is a benign proliferative lesion of the breast stroma characterized by slit-like pseudovascular spaces lined by bland spindle cells, typically presenting as a palpable breast mass in premenopausal women. 1

Clinical Presentation

• PASH most commonly presents as a palpable breast mass that is clinically indistinguishable from a fibroadenoma, with 96% of patients presenting with either imaging-detected or clinically palpable masses 2
• The typical patient is a premenopausal or perimenopausal woman, though rare cases occur in men (particularly those on hormone therapy or with gynecomastia) 2
• Tumor size ranges from 0.3 cm to 7.0 cm, though PASH is more frequently an incidental microscopic finding in breast biopsies performed for other reasons 1, 2
• Lesions are typically unilateral and well-circumscribed with a firm white-gray cut surface on gross examination 1

Pathological Features

• Microscopically, PASH shows a spectrum of stromal changes ranging from classic anastomosing slit-shaped pseudovascular spaces lined by flat, bland spindle cells to more proliferative lesions with bundles of plump spindle cells 1
• The spindle cells are myofibroblastic in origin, demonstrating vimentin and CD34 positivity, with factor VIII negativity 1
• In more cellular lesions, stromal cells acquire desmin and actin positivity, confirming myofibroblastic differentiation 1
• Hormonal receptor staining shows 95% of cases are ER or PR positive, with progesterone receptor reactivity typically exceeding estrogen receptor expression, supporting a hormonal basis for development 1, 2

Diagnosis

• Diagnosis can be made by core needle biopsy (42% of cases) or surgical excision (58% of cases), with some patients requiring both techniques for definitive diagnosis 2
• Imaging modalities including ultrasound, mammography, and MRI can detect PASH, though no distinguishing imaging features reliably differentiate it from other benign breast lesions 3, 2
• Ductoscopy has been successfully used to visualize intraductal PASH in select cases 3

Management and Prognosis

• Simple excision is adequate treatment for most cases, with observation being an option for patients not at high risk for breast cancer 2
• Recurrence occurs in approximately 20% of cases (5 of 24 patients in one series had ipsilateral recurrences), with some patients developing contralateral PASH 1
• Diffuse or recurrent PASH occasionally requires more aggressive management, including reduction mammoplasty or, rarely, bilateral mastectomy for refractory cases 4, 1
• One reported case showed spontaneous regression after incomplete excision, suggesting variable biological behavior 1

Important Caveats

• Malignant transformation is extraordinarily rare, with only one reported case of PASH with foci of morphologic malignancy in the literature, representing a rare sarcoma derived from specialized hormonally responsive mammary stroma 5
• Synchronous breast cancer can occur, as demonstrated by one patient with concurrent DCIS, necessitating careful pathological evaluation of all tissue 2
• The pathogenesis likely involves aberrant myofibroblast reactivity to endogenous or exogenous hormones, explaining its predominance in hormonally active women 1