A Canadian real-world, multi-center, prospective, observational study assessing the treatment duration, the treatment sequence, and the overall survival for patients treated with endocrine therapy ± targeted therapy in HR + HER2-negative advanced breast cancer.

Purpose: Understanding real-world treatment patterns and their effectiveness in HR + HER2- advanced breast cancer (aBC) in Canadian patients.

Patient and methods: This was a multi-center, observational, prospective cohort study including men and pre-/peri-/postmenopausal women with HR + HER2- aBC receiving endocrine therapy (ET) or ET + targeted therapy (ET + TT). The primary objective was duration of treatment (DOT) with ET and ET + TT. Sequence of therapies, treatment patterns, and Overall Survival (OS) were also evaluated.

Results: DOT was prolonged in patients receiving ET + TT compared to ET (median DOT: ET + TT 397 days vs ET 192 days; Log-Rank test p value < .0001; HR = 0.66; 95% CI; 0.52, 0.85). An extended DOT was observed in ET + CDK4/6i subgroup when compared to ET (median DOT: ET + CDK4/6i 601 days vs ET 192 days; Log-Rank test p value < .0001). This increase was statistically significant irrespective of line of therapy at baseline (1L: median DOT: ET + CDK4/6i: 649 days vs ET: 217 days, p value =  < .0001; 2L: median DOT: ET + CDK4/6i: 487 days vs ET: 203 days, p value = 0.0013; 3L: median DOT: ET + CDK4/6i: 597 days vs ET: 143 days therapy: p value = 0.0006). ET alone and ET + CDK4/6i were the most frequently administered therapies in both 1st (ET alone: 43.5% and ET + CDK4/6i: 43.3%) and 2nd lines (ET alone: 36.3% and ET + CDK4/6i: 24.6%). Among patients who received at least one CDK4/6i in 1st, 2nd, or 3rd line, CDK4/6i were mostly administered in 1st line (61.9%) and 2nd line (38.5%).

Clinicaltrials: gov ID: NCT02753686; Registration Date:20-04-2016.

Conclusion: Results support current treatment recommendations of early introduction of CDK4/6i in HR + /HER2- aBC.