Real-world treatment patterns and outcomes of patients with hormone receptor-positive/HER2-low metastatic breast cancer treated with chemotherapy.

Introduction: Hormonal therapy (HT) based regimen is the preferred first-line (1L) treatment for hormone receptor-positive (HR+) metastatic breast cancer (mBC) with human receptor epidermal growth factor 2 (HER2)-low expression. However, HT resistance frequently emerges with many receiving subsequent chemotherapy (CT). This study aimed to examine CT treatment patterns and outcomes among patients with HR+/HER2-low mBC.

Patients and methods: Patient characteristics and clinical data of adults receiving CT for HR+/HER2-low mBC were collected via physician-abstracted chart review from 10/1/2021 to 1/31/2022. Data were summarized using descriptive statistics with the Kaplan-Meier method to estimate time-to-event outcomes. Statistical comparisons were conducted between patients who received 1L CT vs CT after HT-based regimens (any line).

Results: Two hundred and twenty three HR+/HER2-low patients were included, and CT utilization was described by line within metastatic setting: 1L = 20.2% (n = 45), 2L 26.4% (n = 59), 3L+ = 53.4% (n = 119). A higher rate of visceral metastases (86.7% vs 65.7%, P = .01) and lower Eastern Cooperative Oncology Group (ECOG) score (88.9% vs 70.2%, P = 0.01) were associated with 1L CT vs CT post-HT-based treatment. The median time-to-treatment discontinuation (TTD) and real-world progression free survival (rwPFS) of CT were similar between the groups (TTD: 6.7 months vs 8.3 months for the 1L CT and CT post-HT-based regimen groups, respectively, P = .13; rwPFS: 9.3 months vs 8.8 months, P = .26).

Conclusion: In this sample of HR+/HER2-low mBC patients, most patients switched to CT after two lines of therapy with a median rwPFS shorter than 10 months. The findings highlight unmet needs for a more effective targeted therapeutic alternative to CT for HR+/HER2-low mBC patients.