[A Case of Hormone Receptor-Positive Recurrent Breast Cancer Successfully Treated with Low-Dose Ethinyl Estradiol].

The patient, an 83-year-old woman, was diagnosed with ER- and PgR-positive left breast cancer(T2N0M0, Stage ⅡA) at the age of 68. At the time, she underwent preoperative chemotherapy followed by Bp+Ax and postoperative radiotherapy to the conserved breast. She also received endocrine therapy as adjuvant therapy. At the age of 73, she underwent radiotherapy for multiple bone metastases and left axillary lymphadenectomy due to left axillary lymph node recurrence. After surgery, she received 4 regimens of endocrine therapy over a period of 5 years and 1 month for bone metastases. At the age of 79, S-1 was administered for pulmonary metastasis which continued for the next 2 years and 8 months. At the age of 81, palbociclib+letrozole were administered for 1 year and 8 months owing to the progression of bone metastases. At the age of 83, she developed liver metastases and was administered ethinyl estradiol, starting at 1.5 mg/day and continued at a reduced dose of 0.5 mg/day for 9 months. The reduction in tumor markers after treatment initiation was rapid, and there were no serious adverse events. Ethinyl estradiol was useful for maintaining QOL in this elderly patient with recurrent breast cancer.