What is the diagnosis and management of pseudoangiomatous stromal hyperplasia (PASH) of the breast in premenopausal women?

Pseudoangiomatous Stromal Hyperplasia (PASH) of the Breast

What is PASH?

PASH is a benign, hormonally-responsive mesenchymal proliferative lesion of the breast that predominantly affects premenopausal and perimenopausal women, presenting most commonly as a palpable mass or incidental imaging finding that mimics fibroadenoma. 1, 2

• PASH occurs in approximately 95-96% of premenopausal or perimenopausal women, with rare cases in postmenopausal women on hormone replacement therapy 1, 2
• The lesion demonstrates positive staining for estrogen and progesterone receptors in 95% of cases, supporting its hormonal etiology 2
• Approximately 53% of patients present with abnormalities on screening mammography, while 44% present with palpable masses 1

Clinical Presentation

Document the following specific features during physical examination:

• Mass characteristics: Well-defined, discrete margins with round or oval shape on palpation 3
• Size measurement: Lesions range from 0.3 cm to 11 cm in reported series 2, 4
• Growth pattern: Note any documented increase in size over time, as 5 of 7 patients in one series showed progressive growth 4
• Patient age and hormonal status: Median age is 45 years (range 12-65), with 95% occurring in premenopausal women 5

Imaging Features

PASH appears similar to fibroadenoma on all imaging modalities, making definitive diagnosis impossible without tissue sampling. 1

Mammography

• Noncalcified, circumscribed mass in most cases 1, 4
• Border characteristics vary: well-circumscribed (43%), partly circumscribed (29%), or indistinct (29%) when obscured by overlying parenchyma 4

Ultrasound

• Oval, circumscribed, hypoechoic solid mass 1, 4
• All four lesions visible on ultrasound in one series were solid and circumscribed 4

MRI

• Progressive (Type 1) enhancement pattern 1
• High-signal slit-like spaces on T2-weighted and STIR images corresponding to empty clefts within acellular hyalinized stroma 1

Diagnostic Approach

Core needle biopsy is the preferred initial diagnostic method, but has a 35% false-negative rate for PASH, requiring surgical excision for definitive diagnosis in many cases. 5

Biopsy Strategy

• Core needle biopsy confirmed PASH diagnosis in only 65% of cases in one large series 5
• The remaining 35% required operative excision for definitive diagnosis 5
• All pathologic specimens should be reviewed by an experienced pathologist aware of the mass lesion, as PASH can be mistaken for low-grade angiosarcoma 1, 4

Critical Pathologic Distinction

• PASH has pseudoangiomatous slit-like clefts (not true vascular spaces) distinguishing it from angiosarcoma 1
• Staining for CD34 and lymphatic marker D2-40 helps confirm diagnosis 2

Management Algorithm

For biopsy-proven PASH with concordant imaging (BI-RADS 2-3), observation with 6-month interval imaging is appropriate; surgical excision is indicated for growth, suspicious radiologic features, inconclusive biopsy, larger lesions, or patients at increased breast cancer risk. 1, 5

Observation Criteria (All Must Be Met)

• Core biopsy confirms PASH diagnosis 5
• No suspicious radiologic features 5
• Concordance between pathology and imaging 3
• Patient not at high risk for breast cancer 2

Follow-up Protocol for Observed Lesions

• Imaging at 6-month intervals initially 5
• Continue surveillance given recurrence rates of 13-26% 5
• Two patients in one series developed local recurrence 4

Indications for Surgical Excision

• Growth documented on serial imaging or physical examination 4, 5
• Suspicious radiologic findings 5
• Inconclusive or negative core biopsy (35% of cases) 5
• Larger lesions (no specific size cutoff defined, but consider excision for masses >2 cm based on fibroadenoma guidelines) 3, 1
• Patients at increased risk for breast cancer 1, 2
• Patient anxiety or request for removal 3

Surgical Technique

• Local excision with tumor-free margins 2
• Meticulous hemostasis and specimen orientation for pathologist 6

Associated Findings and Cancer Risk

PASH may coexist with breast cancer or precancerous lesions in 30% of cases, mandating careful evaluation of all tissue. 5

• One patient had synchronous ductal carcinoma in-situ (DCIS) 2
• Additional benign findings include stromal fibrosis and atypical ductal or lobular hyperplasia 2
• If atypical features are found on final pathology, follow risk-reduction guidelines per NCCN 3, 7

Common Pitfalls to Avoid

• Do not rely on imaging alone to exclude malignancy: PASH mimics fibroadenoma and cannot be distinguished radiologically 1
• Do not assume negative core biopsy excludes PASH: 35% require surgical excision for diagnosis 5
• Do not ignore documented growth: This warrants surgical excision regardless of benign appearance 4, 5
• Do not forget to assess for concurrent pathology: 30% have associated cancer or precancerous lesions 5
• Ensure pathologist is aware of mass lesion: PASH can be missed or misdiagnosed as angiosarcoma without clinical correlation 1, 4

Recurrence and Long-term Outcomes

• Progression rate: 26% in observation arm versus 13% in excision arm 5
• Local recurrence occurs in 13-26% of cases, necessitating close surveillance 5
• If simple PASH is confirmed without atypia, return to routine age-appropriate screening after initial surveillance period 3