250P Evolution of characteristics, real-world (rw) treatment (tx) landscape, and survival outcomes in patients (pts) with previously untreated metastatic triple-negative breast cancer (mTNBC) in the United States

Immune-checkpoint inhibitors (ICIs) and poly (ADP-ribose) polymerase inhibitors (PARPi) have improved efficacy in clinical trials and expanded the tx options in pts with previously untreated mTNBC. Evolving tx options for early TNBC have decreased relapse rates and improved survival. This study aims to describe how changes in the tx landscape translate into the rw setting in the United States. This retrospective observational study used Flatiron Health electronic health record data. Adult pts initiating first-line (1L) tx for mTNBC (Jan 2011-May 2022) were included. A stratified analysis by period of mTNBC diagnosis was conducted before (2011-2017, early cohort) and after (2018-2022, late cohort) approval of PARPi and ICIs. Pt characteristics, tx received, and outcomes (rw overall survival [rwOS]; time to next tx or death [TTNTD]) were described for each cohort. Of the 2004 pts who initiated 1L tx, 53% and 47% were diagnosed with mTNBC before and after 2018, respectively. Most were treated in community settings as expected (early: 89%; late: 83%). The proportion of pts with obesity (early: 34%; late: 38%), aged ≥ 65 years (early: 34%; late: 43%), and with de novo mTNBC (early: 27%; late: 33%) increased over time. In the early cohort, 97% of pts were treated with chemotherapy (CT; single-agent: 53%; combination: 44%). From 2019, ICI use increased to 33% on average and CT use decreased to 65% (single-agent: 40%; combination: 25%); PARPi use was < 2%. Median rwOS [95% CI] and median TTNTD were comparable between cohorts (early: 10.9 mo [10.3-11.6]; late: 11.9 mo [10.7-13.1] and early: 4.4 mo [4.1-4.8]; late: 4.2 mo [3.8- 4.5], respectively). Of the pts with 1L tx, 53% and 50% subsequently received second-line (2L) tx in the early and late cohorts, respectively; 40% and 34% did not survive. This rw analysis confirms the poor prognosis of previously untreated mTNBC. Despite introduction of ICIs and PARPi, rwOS and TTNTD were comparable before and after 2018. Attrition rates between 1L and 2L treatment remain high. These data demonstrate the unmet need for more efficacious treatments in 1L mTNBC.