Postdoc Department of Clinical Epidemiology, Department of Clinical Medicine, Aarhus University and Aarhus University Hospital, Aarhus, Denmark Aarhus N, Denmark
Background: Premenopausal women with low socioeconomic position (SEP) have higher mortality rates after estrogen receptor positive (ER+) breast cancer than women with high SEP. Low adherence to adjuvant endocrine therapy (AET) can increase recurrence and mortality after ER+ breast cancer but it is not clear if AET adherence is lower in women with low SEP compared with those with high SEP.
Objectives: We investigated the association between SEP and AET adherence in premenopausal women with ER+ stage I-III breast cancer.
Methods: Using Danish population-based administrative and medical registries, we assembled a cohort of premenopausal women diagnosed with stages I-III, ER+ breast cancer during 2002-2011 in Denmark. SEP indicators—cohabitation (cohabiting; living alone), education (short [9-11years]; medium [12-13 years]; long [14-20 years]), household income (low [Q1]; medium [Q2-3]; high [Q4]), and employment (employed; on health-related leave; unemployed)—were ascertained from national registries up to two years before diagnosis. In Denmark, AET is provided free of charge at each biannual follow-up hospital visit after breast cancer diagnosis and is registered in the Danish Breast Cancer Group database. We used group-based trajectory modelling to describe the dynamic patterns of AET adherence over 4.5 years following AET initiation. We estimated the associations of the SEP indicators with each AET adherence group using multinomial regression, with adjustment for covariates specified in directed acyclic graphs.
Results: In a cohort of 4,100 patients, we identified three adherence groups: 3,395 (83%) had consistently high adherence (high adherers); 385 (9%) had high adherence up to 3 years and then declined (slow decliners); and 320 (8%) declined shortly after AET initiation (rapid decliners). Women with lower SEP had higher odds of being rapid decliners. Odds ratios (ORs; 95% confidence intervals [CI]) were 1.57 (1.22, 2.03) among those living alone vs. cohabitating; 1.45 (1.07, 1.96) among those with short vs. long education; 1.33 (0.92, 1.91) among those with low vs. high household income; and 1.70 (1.33, 2.18) for those on health-related leave and 2.65 (1.72, 4.08) for unemployed, both vs. employed women. The ORs for being a slow decliner were also higher among women living alone, with low income, on health-related leave, or unemployed compared with women with high SEP.
Conclusions: Adherence to AET was more often suboptimal in women with low compared with high SEP. This may partly explain the higher mortality rate after premenopausal breast cancer in women with low SEP. Interventions are needed to support women with low SEP at risk of declining AET adherence.
