Effective Hormone Therapy Reduces the Efficacy of Subsequent Chemotherapy in Hormone-Receptor-Positive Metastatic Breast Cancer

Objective: Hormone Therapy (HT) is usually introduced to patients with hormone-receptor-positive metastatic breast cancer without life-threatening metastasis prior to chemotherapy. Many physicians expect HT not to affect the efficacy of subsequent chemotherapy, but there is no evidence to confirm this. In this retrospective study, we investigated the efficacy of chemotherapy after hormone therapy for metastatic breast cancer. Methods: Patients who received chemotherapy after hormone therapy for metastatic breast cancer between 2004 and 2014 at our institution were reviewed, and the efficacy of HT and the efficacy of subsequent chemotherapy were evaluated based on the tumor response and the duration of the therapy. If multiple-line therapies were introduced, the efficacies were evaluated by the best response, longest duration among therapies, and total duration of therapies, and we analyzed the relationship between the efficacies of HTs and chemotherapies. Results: Twenty-nine patients were eligible. The median patient age was 60 years old. The major metastatic sites included bone (17 patients), the lungs (10 patients), and lymph nodes (10 patients). The clinical benefit (CB) rate of all HTs was 62% and the patients received HTs for a median of 20.4 months. Meanwhile, the CB rate of all chemotherapies was 79%, and the patients received chemotherapies for a median of 24.8 months. The CB rates, the longest durations, and the total durations of prior HTs were not associated with the efficacy of subsequent chemotherapy. However, the total duration of the chemotherapies in the patients with very effective HTs (total duration of HTs>20 months, longest duration of HT>14 months, and HTs with CBs) was significantly shorter than for the others (MST 13.1 m vs. 26.8 m; p=0.035). Conclusions: These results suggest that the efficacy of chemotherapies was reduced after very effective HTs.