A comparison of treatment allocation and survival between younger and older patients with HER2-overexpressing de novo metastatic breast cancer

Abstract

Introduction: There have been several developments in the treatment of HER2-overexpressing metastatic breast cancer. However, pivotal trials mainly included younger and healthier patients, resulting in a lack of information about the benefits and harms of treatment for most older patients. The aim of this study was to provide an overview of the differences in treatment allocation and survival outcomes over time between younger and older patients with HER2-overexpressing metastatic breast cancer.

Materials and methods: All patients from the Netherlands Cancer Registry with de novo metastatic breast cancer between 2005 and 2021 were included. Patients were divided into three age groups: <65, 65-74, and ≥ 75 years. Changes in treatment allocation were graphically depicted over time. Cox proportional hazard models were used to calculate overall survival and Poisson models for relative survival.

Results: Overall, 2,722 patients were included. Between 2005 and 2021, the use of targeted therapy as first-line treatment increased for all age groups (<65 years from 33.8% to 90.6%, p < 0.001; 65-74 years from 29.2% to 86.5%, p = 0.001; ≥75 years from 4.3% to 55.8%, p < 0.001). Use of chemotherapy as first-line treatment also increased for all age groups (<65 years from 73.5% to 89.8%, p < 0.001; 65-74 years from 50.0% to 78.4%, p = 0.01; ≥75 years from 8.7% to 37.2%, p = 0.04). Although not statistically significant, the use of endocrine therapy, both as monotherapy and in combination with targeted therapy in the first line, decreased (<65 years 19.1% to 5.5%, p < 0.001; 65-74 years 25.0% to 13.5%, p = 0.03; ≥75 years 65.2% to 37.2%, p = 0.16). Changes in relative and overall survival were similar and improved in all age groups, but most in the youngest age group (relative excess risk [RER] 0.93, 95% confidence interval [CI] 0.91-0.94 per year, p < 0.001), and least in patients ≥75 (RER 0.96, 95% CI 0.93-0.98 per year, p = 0.001).

Discussion: The use of first-line chemotherapy and targeted therapy increased in all age groups, while the use of endocrine therapy decreased over time. Nevertheless, the uptake of chemotherapy and targeted therapies was substantially slower in the oldest age group. Overall survival and relative survival improved for all age groups, but these improvements were smaller in the older age groups.

Keywords: Breast cancer; Epidemiology; HER2-positive; Metastatic; Targeted therapy.