Periductal stromal tumor of breast: a case report and a review of literature.

Periductal stromal tumor (PDST) is a rare biphasic tumor of the breast that exhibits low-grade malignancy and intermediate behavior. It is characterized by proliferation of atypical spindle cells surrounding benign mammary ducts and infiltrating adjacent adipose tissue. PDST is distinguished from phyllodes tumor by its lack of leaf-like architecture; however, it is still unclear whether PDST is a separate entity or a certain spectrum of phyllodes tumor [1,2]. Its therapeutic management is based on wide surgical excision with tumor-free margins. We report the case of a 20-year-old female who presented with a lump in her left breast with clinical features mimicking fibroadenoma. Excisional biopsy was performed because the mass gradually enlarged and became painful. On histological examination a biphasic tumor composed of benign epithelial ducts surrounded by proliferation of spindle cells with dense hyperchromatic nuclei and mild-to-moderate atypia was found. Stromal overgrowth, variable stromal cellularity and myxoid background were evident. A diagnosis of PDST was established after extensive sampling and immunohistochemical analysis. Our patient was treated with surgical resection and has been recurrence-free for more than 38 months.