Abstract PO2-17-01: Impact of the introduction of CDK4/6 inhibitors on treatment duration in patients with HR+, HER2– advanced breast cancer: Final analysis of TreatER+ight, a Canadian prospective, real-world, observational study

Abstract Background: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) are the established first-line targeted therapy (TT) for patients with hormone receptor-positive (HR+), human epidermal growth factor receptor-2-negative (HER2–) advanced breast cancer (ABC). TreatER+ight, the first prospective, real-world study evaluating the treatment patterns, safety and effectiveness of ET alone or ET + TT in Canadian patients with HR+, HER2– ABC (2016 to 2020) recorded ET as the standard of care (SOC) in the first interim analysis report. However, treatment with CDK4/6i combined with ET have rapidly evolved as the SOC in the metastatic setting. Methods: This prospective, multicenter, observational study (NCT02753686) enrolled patients with HR+, HER2‒ ABC with or without prior exposure to ET and up to one line of prior CT in the advanced setting. The patients were enrolled by the line of their therapy (first-line, second-line or third-line) and grouped into 2 cohorts (ET and ET + TT). Duration of therapy, and overall survival (OS) are estimated using Kaplan–Meier method. Here, we report the final outcome with CDK4/6i treatment evolution with sequencing strategy and duration in routine clinical practice. Results: At data cutoff (December 1, 2022), a total of 439 enrolled patients (ET, n=104; ET + TT, n=335) from 25 centers in Canada, constituted the full analysis set. The median age (range) was 71. 5 (37. 0–96. 0) years in ET cohort and 65. 0 (23. 0-87. 0) years in ET + TT cohort. About 84. 6% and 66. 4% were postmenopausal patients in the ET and ET + TT cohorts, respectively. Patients with ECOG PS scores 0 to 1 composed of 82. 0% and 93. 5% in the ET and ET + TT cohorts, respectively. In the overall population, ET alone and ET + CDK4/6i were the most common treatment received by patients in first-line (43. 5% and 43. 3%) and second-line (36. 3% and 24. 6%) treatment settings. In third-line treatment setting, CT was the most common treatment received by patients (38. 4%). Conclusions: Data from final analysis of TreatER+ight have further confirmed the evolution to primary use of CDK4/6i-based combination therapy in the first-line setting for Canadian patients with HR+, HER2– ABC. Additional details on duration of therapy by CDK4/6i agents, overall survival data and age subgroup analysis will be presented at SABCS 2023 Table 1Baseline characteristics, treatment patterns, and duration of treatment Citation Format: Catherine Doyle, Ana Elisa Lohmann, Nayyer Iqbal, Jan-Willem Henning, Swati Kulkarni, Nadia Califaretti, John Hilton, Cristiano Ferrario, Nathaniel Bouganim, Mihaela Mates, Stephanie Guillemette, Ricardo Leite, Stephen Chia. Impact of the introduction of CDK4/6 inhibitors on treatment duration in patients with HR+, HER2– advanced breast cancer: Final analysis of TreatER+ight, a Canadian prospective, real-world, observational study abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84 (9 Suppl): Abstract nr PO2-17-01.