Background: Pseudoangiomatous stromal hyperplasia (PASH) is a benign mesenchymal proliferative lesion of the breast. Owing to the rarity of PASH, the pathogenesis, clinical manifestation, and optimal treatment of this condition remain unclear. We aimed to clarify the appropriate management of PASH. Methods: We performed a retrospective analysis of the clinicopathological data of 66 cases with a diagnosis of PASH, confirmed by core needle biopsy (CNB) or surgical excision at Severance Hospital between 2000 and 2016. The primary endpoint was pathologic results after surgical excision of the lesion that confirmed PASH by CNB. The secondary endpoint was progression after the first treatment. Result: The median age of patients was 41 years (range, 14–61 years). Findings on medical imaging were nonspecific. CNB was performed in 61 cases, with a diagnosis of PASH confirmed in 39 cases (63.9%). No malignant or premalignant cells directly arising from PASH were identified after surgical excision that confirmed PASH via CNB. The progression rate after the first treatment was 16.6%, with lesion size, enlargement of palpable mass size, and a diagnosis other than PASH on CNB being factors associated with progression. Conclusion: CNB is sufficient to confirm PASH what is necessary for an abnormal imaging or suspicious physical examination finding. Surgical excision is not necessarily indicated to rule out occult malignancy after a diagnosis of PASH. Close monitoring or surgical excision are required to manage large lesions (>3 cm) or progressive growth of a PASH lesion.
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