Background
The treatment landscape for metastatic triple-negative breast cancer (TNBC) is evolving. While chemotherapy remains common, immune checkpoint inhibitors and antibody-drug conjugates (ADCs) are new options in earlier treatment lines. Real-world evidence on treatment patterns beyond first-line in the US community setting is limited. Understanding these patterns is critical for optimizing care.
Methods
Patients from N-Power Medicine’s Real-World Breast Analytical Dataset receiving care in the US community setting, diagnosed with metastatic TNBC between January 1, 2018, and December 31, 2023, who received 2 or morelines of therapy, had no clinical trial participation, did not receive treatment indicative of HER2-positive or estrogen receptor–positive disease, and had 1 or more years of follow-up, were evaluated. Patient demographics, clinical features, biomarker testing, and treatment patterns were described.
Results
A total of 145 patients (median age: 56 years, interquartile range [IQR] 46-65; median follow-up: 17 months, IQR 11–25) with de novo (50%) or recurrent (50%) metastatic TNBC were included. Most recurrences occurred after adjuvant therapy (34%) or with unknown/no adjuvant therapy (44%). Central nervous system metastases were more frequent in patients with recurrent than de novo tumors (26% vs 7%).
PD-L1 testing, which most frequently occurred after metastatic TNBC diagnosis and before first-line therapy, was high (81% de novo; 77% recurrent) and increased over time (59% in 2018 to 82% in 2022). Germline BRCA1/2 testing rose from 59% (2018) to 92% (2023); patients with recurrent TNBC were often tested in the early-stage setting (79%). As part of routine HER2 testing, HER2-low (immunohistochemistry 1+ or 2+ with non-amplified in-situ hybridization) was identified for most patients (97% de novo; 68% recurrent) after metastatic TNBC diagnosis and prior to first-line.
Chemotherapy with or without PD-L1 inhibitors were the most common second-line therapy (82%), while ADC use was limited (10%). Among patients who received second-line therapy, 53% received 3 or more lines of therapy. Chemotherapy with or without PD-L1 inhibitors remained the most common therapy in third-line (63%), but ADC use increased to 26% in third-line. Additionally, 28% of patients received fourth-line therapy (Figure). Among 55 HER2-low patients, 36% received an ADC and 7% received more than 1 ADC.
Conclusion
In this real-world cohort of 145 patients with metastatic TNBC receiving 2 or more lines of therapy, chemotherapy often with immunotherapy remained the predominant treatment across later lines. While more than half of patients received 3 or more lines of therapy, ADC uptake was modest and primarily observed in third-line or beyond. These findings highlight the continued reliance on chemotherapy in the US community setting despite the advent of improved therapeutic options, underscoring the need for improved access to and integration of emerging therapies earlier in the treatment sequence.
