Treatment patterns and outcomes in HER2-low metastatic breast cancer patients previously treated with chemotherapy: a US real-world cohort study.

Purpose: Real-world outcomes are poorly understood for patients with human epidermal growth factor receptor 2 (HER2)-low (immunohistochemistry 1+ or 2+ with negative in situ hybridization) metastatic breast cancer (mBC).

Methods: Using for the first time a nationwide electronic health record-derived de-identified database, we assessed demographics, treatment patterns, and outcomes of patients with HER2-low mBC who previously received one line of chemotherapy in the metastatic setting. The post-chemotherapy line was termed the index line of therapy (LOT).

Results: 3765 patients [hormone receptor (HR)-positive: 78.8%, HR-negative: 21.0%] met the inclusion criteria (1 January 2011-30 April 2023). 61.7% of HR-positive patients received endocrine therapy prior to the index LOT. The largest patient percentage received single-agent chemotherapy at the index and subsequent two LOTs. For the overall cohort, the median real-world time to treatment discontinuation/death was 4.1 months (95% CI: 3.9-4.2) and the median real-world time to next treatment/death was 5.1 months (95% CI: 4.8-5.3) from the index LOT. Median real-world overall survival (all patients) was 15.8 months (95% confidence interval: 15.2-16.5, median follow-up = 54.5 months) from the index LOT.

Conclusion: These data highlight the unmet clinical needs of patients with HER2-low mBC by characterizing the treatment patterns and poor outcomes in this population on the current standard of care.