This study aimed to evaluate treatment patterns and clinical outcomes in patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (mBC) initiating at least one chemotherapy for metastatic disease in real-world settings in Japan.

In this observational retrospective cohort study, data of 2697 patients with HR+/HER2- mBC from a Japanese medical claims database who initiated the first chemotherapy in metastatic setting between January 1, 2017, and March 31, 2022, were analyzed. The study assessed treatment patterns, time to next treatment or death (TTNTD), time to treatment discontinuation, medical costs, and adverse events of interest for those receiving first-, second-, and third-line chemotherapies for mBC.

The most common regimens were S-1 (20.1%), eribulin (12.2%), and paclitaxel + bevacizumab (6.9%) for each line of therapy, respectively. The TTNTD decreased as treatment advanced, with medians of 8.2, 7.3, and 6.0 months for each line. Monthly medical costs were 277.1, 340.9, and 378.4 thousand yen for each line of therapy, respectively. Nausea/vomiting and neutropenia/leukopenia occurred in 62.6% and 20.5% of patients, respectively.

This study highlights current chemotherapy practices for HR+/HER2- mBC in Japan, where treatment patterns largely align with clinical guidelines but vary according to patient characteristics. Notably, the TTNTD shortens with successive treatments, and medical costs increase, intensifying the financial burden on patients. These findings indicate unmet needs for improved treatment options that enhance outcomes and reduce patient burden in advanced therapy lines.