Background: HR+/HER2- mBC remains incurable, despite progress made with endocrine therapy (ET) + CDK4/6i in prolonging survival. After resistance to ET-based treatment, options are limited to CT and a decrease in survival is observed with every subsequent line of treatment received. This study describes real-world outcomes in pts with HR+/HER2- mBC initiating CT or previously treated with CT in the US. Methods: This retrospective, observational cohort study used the ConcertAI Patient360™ curated dataset of electronic medical record data from the US. Pts (≥18 years) diagnosed with HR+/HER2- mBC and initiating their first CT from January 2011 to June 2021 were included. Real-world outcomes were assessed for all pts who initiated treatment with a first CT, and those who were subsequently treated with a second, third, and fourth CT. Index date was defined as the CT start date of each systemic therapy line. Results: In total, 1545 pts met the eligibility criteria and were included for analysis. Pts were primarily female (99%) and White (76%); median age was 61 years (IQR, 52-69) and 68% had visceral metastases. Most pts (80%) were treated in a community setting and 41% received their first CT in 1L; 58% and 44% had prior exposure to ET and CDK4/6i in the mBC setting, respectively. The median time from mBC diagnosis to first CT was 12 months (IQR, 1.4-30.8). Among all pts included, 57%, 31% and 17% were subsequently treated with a second, third, and fourth CT, respectively, during the study period. Capecitabine and paclitaxel were the most used as the first (45% and 29%), second (35% and 30%), and third (25% and 22%) CT, while gemcitabine (22%) and eribulin (20%) were used most as fourth CT. Clinical outcomes assessed are summarized in the table. Median real-world overall survival (rwOS; 95% CI) from time of mBC diagnosis was 48.5 months (45.5-51.5). Median rwOS from first CT treatment start date was 23.3 months (21.3-25.4). In pretreated pts with 1, 2, or 3 prior lines of CT, median rwOS from each index date was 16.5 months (14.8-18.3), 11.8 months (10.4-13.1), and 9.1 months (7.3-11.2), respectively. Conclusions: Among pts with HR+/HER2- mBC in this analysis, CT choice and real-world clinical outcomes per systemic therapy line were comparable to existing literature. Outcomes decreased as pts advanced CT lines, indicating that in this setting the unmet need remains high. More efficacious treatment options are needed for ET-resistant, chemo-naïve pts and pts pretreated with CT with HR+/HER2- mBC.

^aFrom index date, defined as the CT start date of each systemic therapy line received.