Incidentally Discovered Extensive Squamous Metaplasia within Borderline Phyllodes Tumor: Presentation of a Rare Tumor

Phyllodes tumors are uncommon biphasic fibroepithelial neoplasms of breast, comprising less than 1% of all breast neoplasms. We therefore aimed to present the case with its microscopic findings. In this article, we report a 59-year-old female admitted to the general surgery department with a rapidly, enlarging, palpable mass in right breast. After histopathological examination, it was diagnosed as borderline phyllodes tumor with extensive squamous metaplasia. Metaplastic changes are infrequent in the stromal and epithelial component of these tumors. Extensive squamous metaplasia within phyllodes tumor is rare and may occur in benign, borderline and malign subtypes.