[A Case of a Metaplastic Breast Cancer That Grew in a Short Period of Time].

The patient is a 45-year-old woman. She was aware of a right breast mass and consulted a referring physician. She was referred to our department for close examination and treatment. No axillary lymph node metastasis or distant metastasis was suspected on imaging examination, and a diagnosis of right breast cancer(cT2N0M0, Stage ⅡA)was made. The subtype was Luminal type with weakly positive ER. Preoperative chemotherapy was considered, but the patient underwent partial mastectomy and sentinel node biopsy. Histopathologically, the tumor cells were irregular with spindle-shaped nuclei, and the diagnosis of metaplastic breast cancer was made. The postoperative diagnosis was pT2, N0(sn), M0, Stage ⅡA. Metaplastic breast cancer is rare, accounting for approximately 1% of all malignant mammary tumors, and is considered to be a disease with a poor prognosis. There are reports that chemotherapy is ineffective, and there is no established treatment for this disease. We report the treatment course of this case with some discussion of the literature.