Adherence behaviours in breast cancer patients at risk of cardiovascular disease

BACKGROUND: High rates of discontinuation undermine the effectiveness of adjuvant endocrine therapy (AET) among hormone-receptive breast cancer patients. Patient prognosis also relies on the management of cardiovascular (CV) risk, which affects a high proportion of postmenopausal women. As with AET, adherence with CV drugs is suboptimal. We examined whether patient adherence with CV drugs was associated with AET discontinuation in a French nationwide claims database linked with hospitalisation data. METHODS: Women aged over 50 starting AET between 01/01/2016 and 31/12/2020 and taking at least two antihypertensive and/or lipid-lowering drugs were followed for 5 years or until AET discontinuation, 31/12/2021, death or cancer recurrence. Women were categorised as fully adherent, partially adherent or fully non-adherent with their CV drug regimen in the year before starting AET. The primary outcome was AET discontinuation, defined as a 90-day gap in treatment availability. Cumulative incidence curves were used to estimate time to discontinuation according to CV drug adherence and accounting for competing risks of death and cancer recurrence. Multivariate Cox and Fine-and-Gray regressions were used to assess the relative hazards of AET discontinuation while adjusting for potential confounders. RESULTS: 32,072 women fit the inclusion criteria. Fully adherent women had the lowest cumulative incidence of AET discontinuation at any point over the follow-up period. Partial adherence and full non-adherence with CV drugs were predictors of AET discontinuation in both models (cause-specific hazard ratios 1.15 [95% CI: 1.15-1.25] and 1.49[95% CI: 1.42-1.63]; subdistribution hazard ratios 1.15[95% CI: 1.09-1.21] and 1.47[95% CI: 1.38-1.57]). CONCLUSIONS: Patients who do not adhere with their CV drug regimen are more likely to discontinue AET. Appropriate support should be brought to these patients as they may be at heightened risk of both cardiovascular and cancer-related events. KEY MESSAGES: • Concurrent management of cardiovascular health and breast cancer is essential and clinicians should know that patients with low adherence to cardiovascular drugs are more likely to discontinue AET. • Patients with suboptimal adherence across their drug regimen should be brought appropriate support as they may be at heightened risk of both cardiovascular and cancer-related events.