Pseudoangiomatous Stromal Hyperplasia of the Breast Diagnosed on Excisional Biopsy: A Case Report

Pseudoangiomatous Stromal Hyperplasia (PASH) is a rare benign mesenchymal lesion of the breast. When PASH presents as a mass lesion, it is referred to as a PASH tumour, which is an uncommon manifestation. In the present case report, the authors describe a 34-year-old woman who presented with a painful lump in the left breast. Mammography revealed a well-defined dense lesion {BIRADS IVa (Breast Imaging-Reporting and Data System Category 4a: Low Suspicion for Malignancy)} in the left breast, raising clinical and radiological suspicion of malignancy. A True-Cut (Tru-cut) biopsy was performed, and microscopic examination showed linear cores of breast parenchyma with a few terminal duct-lobular units. Malignancy was excluded using Immunohistochemistry (IHC), following which wide local excision was undertaken. The excised lesion was diagnosed as PASH. Histopathological examination showed a circumscribed lesion composed of terminal duct-lobular units with ducts and acini lined by inner luminal and outer myoepithelial cells. The stroma demonstrated anastomosing slit-like spaces lined by spindle to oval-shaped cells with bland nuclei, embedded within dense collagen. The spaces were empty. IHC revealed Cluster of Differentiation 34 (CD34) positivity in the spindle cells and Cluster of Differentiation 31 (CD31) negativity, helping to differentiate PASH from vasoformative lesions. The treatment of choice is complete surgical excision, as recurrence may occur following incomplete resection. There is no evidence of malignant transformation in PASH; therefore, accurate diagnosis is important to avoid overtreatment. PASH may occur in association with other breast lesions such as fibroadenoma, sclerosing lobular hyperplasia, and gynaecomastia; hence, careful evaluation for associated lesions with malignant potential is necessary. The present case is reported due to its rare presentation as a PASH tumour.