Real-World Treatment Patterns and Outcomes for Patients With Metastatic Triple-Negative Breast Cancer in the United...

To examine real-world treatment patterns and effectiveness among patients with metastatic triple-negative breast cancer (mTNBC) in the United States.

Retrospective, observational study using Flatiron Enhanced Datamart electronic health records from patients diagnosed with mTNBC between January 1, 2018, and June 30, 2023, who received ≥1 line of therapy (LoT) for metastatic disease. Patients were followed until date of death, last recorded activity, or data cutoff (December 30, 2023). Patient characteristics, treatments received from LoT1-5, and clinical outcomes (overall and by LoT) were described.

The cohort comprised 1,044 patients. Most were female (99.2%); the median age was 61 years (IQR, 52-71); 52.1% were White and 21.7% were Black. The most common drug class in all LoTs was chemotherapy, as monotherapy or in combination with other agents: LoT1 85.5%, LoT2 73.2%, LoT3 65.8%, LoT4 64.7%, and LoT5 71.7%. Among patients with known PD-L1 status (n = 367), 109 (29.7%) were PD-L1-positive and 258 (70.3%) were PD-L1-negative. For the overall cohort, the median real-world overall survival (rwOS) from diagnosis was 14.0 (95% CI, 12.9 to 16.0) months. Real-world progression-free survival was 4.5 (95% CI, 4.0 to 5.0) months in LoT1 and 4.1 (95% CI, 3.5 to 4.9) months in LoT2. The median rwOS was 18.6 (95% CI, 15.2 to 24.4) months in the PD-L1-positive cohort versus 12.7 (95% CI, 11.0 to 16.0) months in the PD-L1-negative cohort. From December 1, 2021, onward, immunotherapy was received in LoT1 by 63.6% (21/33) of patients who had PD-L1-positive tumors and by 84.6% (33/39) of patients with PD-L1-positive tumors across all LoTs.

Real-world clinical outcomes in patients with mTNBC in the United States remain poor, particularly for patients with PD-L1-negative disease. There is an unmet need for more effective treatments for mTNBC.