[First-Line Treatment of Advanced ER-Positive HER2-Negative Breast Cancer in Ikeda City Hospital]

In patients with ER-positive HER2-negative unresectable breast cancer, who are refractory to chemotherapy, surgery may not be performed even after endocrine therapy. CDK4/6 inhibitors have been used as first-line treatment for unresectable breast cancer since their approval in Japan. We investigated the primary treatment of ER-positive HER2-negative inoperable breast cancer and its efficacy in our hospital. 14 patients diagnosed between March 2017 and October 2022 were included. Three patients were treated with endocrine therapy alone(HT), 6 with CDK4/6 inhibitors(all 6 with palbociclib[PAL]), and 5 with chemotherapy(CT). Median age at diagnosis was 83, 74.5, and 67 years, respectively. In the HT group, 2 patients died, 1 patient discontinued due to metastasis. In the PAL group, 2 patients discontinued due to adverse events, 4 patients underwent surgery. All 5 patients in the CT group underwent surgery. In some patients who were refractory to chemotherapy, the combination of CDK4/6 inhibitors reduced tumor size to the extent that surgery was possible, suggesting the effectiveness of this combination as first-line treatment.