A Canadian real world prospective observational study assessing the impact of hormone therapy ± targeted therapy in the treatment of HR+ HER2- 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 an 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 1 ^st (ET alone: 43.5% and ET+CDK4/6i: 43.3%) and 2 ^nd line (ET alone: 36.3% and ET+CDK4/6i: 24.6%). Among patients who received at least one CDK4/6i in 1 ^st , 2 ^nd , or 3 ^rd line, CDK4/6i were mostly administered in 1 ^st line (61.9%) and 2 ^nd 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.