Real-world effectiveness of aromatase inhibitors and fulvestrant in HR+/HER2- advanced breast cancer: a snapshot of the last two years before conventional use of CDK 4/6 inhibitors in a Portuguese institution

Abstract

ABSTRACTBackground: Monotherapy with aromatase inhibitors and fulvestrant were the standard-of-care for hormone receptor-positive (HR+)/human epidermal growth factor receptor-type2 negative (HER2-) advanced breast cancer, before integration of cyclin-dependent kinase 4/6 inhibitors. Effectiveness data is essential for regulatory action, but little is known about real-world use of aromatase inhibitors and fulvestrant.Methods: A retrospective cohort study was conducted resorting to data from a cancer registry to identify adult women with HR+/HER- advanced breast cancer exposed to aromatase inhibitors or fulvestrant (31 May 2017–31 March 2019) at the main oncology hospital in Portugal. Cases were updated with follow-up until death or cut-off (31 March 2021) and pseudoanonymized data extracted. Primary outcome was overall survival (OS) and secondary time to treatment failure (TTF), estimated using survival analysis and compared with published trials.Results: 192 patients were distributed by subgroups according to the medicine. Letrozole: OS 30.8 (95% confidence interval (CI) 20.6–41.4); TTF 11.2 (95%CI 8.7–13.7). Exemestane: OS 22.1 (95%CI 9.7–34.6); TTF 6.0 (95%CI 4.1–7.8). Fulvestrant: OS 21.6 (95%CI 16.5–26.7); TTF 5.6 (95%CI 4.5–6.6).Conclusions: Estimated effectiveness (OS) of letrozole and fulvestrant was, respectively, 3.2–3.5 months lower than reported. The clinical meaning seems uncertain and may be explained a higher proportion of worse prognostic characteristics in patients treated in the real-world.

Keywords

• Advanced breast cancer
• Registries
• Effectiveness
• Fulvestrant
• Aromatase inhibitors