[Successful Treatment of Estrogen Receptor Positive, HER2 Negative Breast Cancer with Life-Threatening Multiple Bone Metastases Using the Combination of Fulvestrant and Palbociclib-A Case Report].

Palbociclib, a CDK4/6 inhibitor, is found to be an effective therapeutic drug in the treatment of estrogen receptor positive (ER+)metastatic breast cancer. In this report, we describe a case of rapid progression of life-threatening multiple bone metastases of breast cancer treated with a combination of fulvestrant and palbociclib. The patient, a 58-year-old postmenopausal woman, was diagnosed with left breast cancer at the age of 43 years and underwent breast-conserving surgery. After the completion of postoperative adjuvant endocrine therapy and radiotherapy, the patient was placed on regular follow-up. Eleven years after the surgery, multiple bone metastases and multiple lymph node metastases occurred, and the patient was treated with letrozole as first-line therapy for recurrent breast cancer. Although she continued to receive this treatment for 2 years and 10 months, her general condition worsened due to the occurrence of new liver metastases and the rapid progression of existing metastatic lesions. Thus, she was sent to an emergency room. Marked hypercalcemia and a severe decrease in erythrocyte and platelet counts were observed, which could be the cause of her worsening general condition. Her performance status(PS)was 4, and palliative treatment was also considered. However, she received treatment for hypercalcemia and red blood cell transfusion; as a result, she recovered to the PS 2 where she could begin chemotherapy. Then, she began a treatment consisting of a combination of fulvestrant and palbociclib as a second-line treatment for the recurrence. The patient responded well to the treatment, and her general condition improved to PS 1. She has since maintained a good quality of life for 2 years and 11 months without serious adverse events. In conclusion, the combination of fulvestrant and palbociclib has a low risk of serious adverse events and is a worthwhile treatment for rapidly progressing, life-threatening multiple bone metastases of breast cancer.