Abstract
A 61-year-old woman noticed a mass in her left breast about one year previously. The tumor was palpable, 40 mm in diameter, and a firm consistency. The fine needle aspiration cytology was indeterminate, while the core needle biopsy revealed ductal hyperplasia. Clinically the tumor had a probability of malignancy, and an excisional biopsy was performed. Pathological examination revealed the tumor to be composed of mammary gland and stroma with spindle cells. Immunohistochemical staining showed that these spindle cells were positive for α-smooth actin, and the diagnosis was myoid hamartoma. The patient has been tumor-free for the past one year. Myoid hamartoma of the breast is a rare breast tumor resembling breast cancer. We must include myoid hamartoma as a differential diagnostic consideration in cases of breast tumor : such as fibroadenoma, phyllodes tumor, leiomyoma, adenomyoepithelioma and fibromatosis, if spindle cells are observed in pathological samples.
