Cohort study of attrition between lines of therapy and real-world outcomes of European patients with HER2-positive metastatic breast cancer

A retrospective cohort study leveraging electronic medical records of patients with HER2-positive metastatic breast cancer (mBC) in five European countries evaluated real-world attrition rates (proportion of patients receiving a line of therapy [LOT] with no evidence of subsequent LOT) across first-line to third-line therapies. The attrition rates were 29.6% (95% CI 25.0-34.6) after first-line treatment and 34.2% (27.5-41.5) after second-line treatment. Attrition was primarily due to death, move to end-of-life palliative care, loss to follow-up, and ‘other reasons’. With each subsequent LOT decreases were observed in time to discontinuation (12.1 months for first line, 8.9 months for second line, and 6.4 months for third line) and time to next treatment (15.4 months for first line and 13.5 months for second line). The authors conclude that these results unveil that a large proportion of patients do not benefit from state-of-the-art subsequent LOTs and suggest diminishing effectivenes of each subsequent LOT.