Compliance with endocrine therapy among breast cancer survivors.

Introduction: Most postmenopausal women with early-stage oestrogen receptor-positive breast cancer are allocated to five years of endocrine therapy. This treatment is not without adverse effects, which may lead to treatment discontinuation. This study aimed to assess compliance with endocrine therapy among postmenopausal women with early-stage oestrogen receptor-positive breast cancer and examine its association with disease-free survival.

Methods: This study retrospectively identified a cohort of 360 postmenopausal women diagnosed in the period from 1 January 2015 to 31 December 2017 at Rigshospitalet, Copenhagen, Denmark, with early-stage oestrogen receptor-positive breast cancer in the clinical database of the Danish Breast Cancer Group. Kaplan-Meier was used to estimate compliance and disease-free survival.

Results: A total of 346 patients receiving endocrine therapy were included, 240 were compliant, and 106 were non-compliant. The median follow-up was 6.5 years (95% confidence interval (CI): 6.4-6.7 years). The compliance at 4.5 years was 68.8% (95% CI: 64.1-74.0%). Disease-free survival was significantly higher for the compliant group (adjusted HR = 2.29; 95% CI: 1.34-3.91).

Conclusions: We found a low compliance at 4.5 years and most discontinuations were due to adverse effects. The study provides evidence that low compliance with endocrine therapy had a negative impact on disease-free survival.

Funding: The study was funded by the Danish Cancer Society.

Trial Registration: The study was approved by the research overview of the Capital of Denmark and the Center for Health.