Factors associated with first-to-second-line attrition among patients with metastatic breast cancer in the real world.

Background: Estimating patient attrition across lines of treatment (i.e. the probability that upon treatment failure the patient will not be able to receive a subsequent treatment) may be a valuable tool for optimizing treatment sequencing. We sought to describe the first-to-second-line attrition rate and factors associated with attrition in a real-world cohort of patients with metastatic breast cancer.

Methods: The Gruppo Italiano Mammella (GIM)14/BIO-META (NCT02284581) is an ongoing, ambispective observational multicenter study enrolling patients with metastatic breast cancer receiving first-line therapy. In patients experiencing disease progression, attrition was defined as no further anticancer treatment and death within 6 months from the end of first-line therapy. The attrition rate from the first-to-second line was studied by descriptive analyses and univariate and multivariable logistic models were used to explore potentially predictive factors.

Results: From January 2000 to December 2021, 3109 patients with metastatic breast cancer were enrolled in the GIM14/BIO-META study. Among them, 2498 patients experienced first-line treatment failure. Overall, first-to-second line attrition was 9.0% (95% confidence interval 7.9% to 10.1%), with similar attrition for patients with hormone receptor-positive/HER2-negative (8.5%) and HER2-positive (7.1%) breast cancer. Patients with triple-negative disease experienced the highest attrition (13.0%). Age, menopausal status, disease-free interval from primary tumor diagnosis, type of metastatic spread, and tumor subtype independently predicted first-to-second-line attrition.

Conclusions: These findings could inform treatment decisions and guide clinical research on treatment sequencing. For instance, patients with the lowest risk of attrition may be the ideal candidates for trials exploring de-escalated first-line regimens, followed by more aggressive treatments upon progression.