A case of tumor-forming pseudoangiomatous stromal hyperplasia of the breast.

Pseudoangiomatous stromal hyperplasia (PASH), characterized by the presence of slit-like spaces embedded in a hyalinized stroma, is sometimes observed during pathologic examination of breast-tissue specimens. Because tumor-forming PASH is rare, we report a case of a 41-year-old woman admitted to our hospital with a tumor in her left breast. Ultrasonography and aspiration biopsy cytology revealed a benign tumor. After performing Mammotome(®) biopsy, the lesion was diagnosed as PASH of the breast based on characteristic findings of histology and immunohistochemical studies. Because PASH tumors do not usually become malignant, we decided to perform ultrasonographic follow-up without tumor excision.