End-of-life Endocrine Treatment of Older Hormone Receptor-positive Metastatic Breast Cancer Patients: A Nationwide Swedish Retrospective Cohort Study

Background: A substantial body of research discusses appropriate chemotherapy discontinuation at the end of life of older metastatic breast cancer patients. However, only a few studies investigate endocrine treatment use near death.

Objectives: To establish how frequently endocrine treatment is continued to the end of life or initiated close to death in metastatic breast cancer patients in Sweden. Additionally, to identify patient characteristics associated with a higher likelihood of end-of-life endocrine treatment and late initiation.

Methods: Longitudinal, retrospective cohort study of decedents, including all older women (aged ≥65 years) with hormone receptor positive (defined as ever use of endocrine treatment) metastatic breast cancer who died in Sweden, 2016-2020. We used national death certificate data individually-linked to several national registries. Endocrine treatment exposure was identified based on the Anatomical Therapeutic Chemical codes (subgroup level ‘L02'). Treatment initiation was defined as the dispensing of endocrine treatment during the last 3 months of life given no endocrine treatment during the prior nine months. Treatment continuation was defined as endocrine treatment dispensing during the last 3 months of life given previous use during the prior nine months. Multivariable logistic regressions were performed to investigate characteristics associated with treatment initiation and continuation.

Results: In total, 3,149 (median age at death 78 years) were included in the study as hormone positive metastatic patients. More than one-third (41%) had ≥6 comorbidities and 11% lived in a nursing home. Endocrine treatment was initiated by 8% and continued to the end of life by 38% of the study population. Endocrine treatment initiation had statistically significantly lower odds among patients with several comorbidities, while women with concomitant CDK4/6 treatment had higher odds. Endocrine treatment continuation had one of the highest odds ratio (3.2, 95% confidence interval: 2.5-4.0) for women with multi-dose dispensing (prescriptions delivered in machine packed pouches). Older women, those with many comorbidities or concomitant CDK4/6 treatment also had higher odds. While those with chemotherapy treatment at the end of life or higher education had lower odds to continue endocrine treatment.

Conclusions: One third continue and 8% of older women with metastatic breast cancer initiate endocrine treatments at the very last part of life, potentially past the point where treatment has a benefit. Our results underscore the importance of continuously re-evaluating patient's treatments close to death.