E-PS-02-026 Pseudoangiomatous stromal hyperplasia of the female breast: a case report

Background & Objective: Pseudoangiomatous stromal hyperplasia (PASH) is a benign myofibroblastic proliferation of the mammary gland, histologically characterized by interanastomosing slit-like lesions lined by spindle cells. Since its first description in 1986, less than 200 cases have been identified as tumour-forming PASH in the English literature. More frequently it localizes in the upper outer quadrant of the right breast. The aim of this study is to report a case of PASH in the axilla of a 20 year-old Caucasian woman. Method: The clinical and ultrasound examination of the right axilla of the patient revealed a subcutaneous nodule of 25x5 mm. An excisional biopsy was performed. Results: Macroscopically, the yellow-whitish nodule had a firm-rubbery consistence. The histological examination revealed spindle stromal cells lining thin empty spaces, without atypias or mitotic figures. There was not involvement of the surrounding adipose tissue. At immunohistochemistry, spindle cells were immunostained with vimentin, smooth muscle actin and CD34. Focal immunoreactivity for estrogen and progesterone receptors was also found, whereas stromal cells were negative for CK AE1/AE3/PCK26, desmin, CD31 and factor VIII. Ki-67 was positive in about 10% of proliferating spindle cells. Conclusion: Tumour-like PASH in the axilla is a rare event. At the best of our knowledge, in women it has been described in five cases. PASH can mimic benign (fibroadenoma, myofibroblastoma, hamartoma) and malignant (phyllodes tumour, angiosarcoma) lesions. An accurate diagnosis is required in order to avoid overtreatment.