[A Case of Breast Metaplastic Carcinoma and Distant Metastasis with Complete Response to Immunotherapy].

An 82-year-old woman visited our hospital complaining of a rapidly growing hemorrhagic mass with ulceration of the right breast. A CT scan revealed a circumscribed, lobulated mass of approximately 14 cm diameter, with coarse calcifications, which had invaded the skin and major pectoral muscle and with metastasis in the both lungs. She underwent a total mastectomy with major pectoral mastectomy. The pathological findings were spindle cell carcinoma admixed with chondroid metaplasia and an osteoid-like appearance; therefore, metaplastic breast cancer was diagnosed. Biweekly drip infusion of immune checkpoints inhibitor were administered as immunotherapy, which yielded a complete response of lung matastasis. Administration of monthly immune checkpoints inhibitor resulted in no recurrence for 3 years after the operation. Accumulation of further similar cases and development of a novel effective treatment are desired.