A comparison of the efficacy of trastuzumab deruxtecan in advanced HER2-positive breast cancer: active brain metastasis versus progressive extracranial disease alone.

Background: Trastuzumab deruxtecan (T-DXd) has demonstrated efficacy in patients with brain metastasis (BM), a group historically with poor outcomes. The prevalence of BMs in patients commencing T-DXd is currently unknown. No direct comparisons have been made of the activity of T-DXd in patients with active BM versus those with extracranial progression alone. This real-world study explored the prevalence of BMs in patients commencing T-DXd, the efficacy of T-DXd in active BM versus extracranial progression alone and the safety of T-DXd.

Patients And Methods: Patients with human epidermal growth factor receptor 2-positive advanced breast cancer treated with T-DXd between June 2021 and February 2023 at our specialist cancer hospital were identified and notes reviewed. Clinicopathological information, prior treatment, the presence or absence of central nervous system (CNS) disease, outcomes and treatment-emergent adverse events (TEAEs) were recorded.

Results: Twenty-nine female patients, with a median age of 52 years (interquartile range 44-62 years), were identified; the prevalence of BM was 41%. Median number of lines of prior therapy was 2 (range 2-6). At a median follow-up of 13.8 months, median progression-free survival (PFS) for the overall population was 13.9 months [95% confidence interval (CI) 12.4 months-not estimable (NE)], 16.1 months (95% CI 15.1 months-NE) for active BMs and 12.4 months (95% CI 8.3 months-NE) for progressive extracranial disease alone. The 12-month overall survival (OS) rate was 74% (95% CI 59% to 95%) in the overall population, and 83% (95% CI 58% to 100%) and 66% (95% CI 45% to 96%) for active BMs and extracranial disease only, respectively. Most common TEAEs were fatigue, alopecia, and constipation. In nine patients (31%, including two deaths), pneumonitis occurred.

Conclusion: In this real-world population, we demonstrate T-DXd to be effective in patients with active BMs and those with progressive extracranial disease alone. PFS and OS were numerically longer in those with active BMs. These data demonstrate that patients with active BM treated with T-DXd have at least comparable outcomes to those with extracranial disease alone. The high rate of pneumonitis warrants further consideration.