6D-05 - Social vulnerability and adherence to adjuvant endocrine therapy in premenopausal women with breast cancer – a Danish population-based cohort study

Background: Adjuvant endocrine therapy (AET) halves the risk of breast cancer recurrence. Yet, up to 30% of Danish patients do not adhere to the recommended five years of treatment. Social vulnerability describes a person’s overall social situation and how it affects susceptibility to poor health, but it is unknown if social vulnerability is associated with AET adherence.

Objectives: To evaluate the association between social vulnerability and AET adherence in premenopausal women with breast cancer.

Methods: Using population-based registries, we assembled a cohort of premenopausal women diagnosed with stage I-III, estrogen receptor positive breast cancer in Denmark (2002-2011). We applied a registry-based social vulnerability index (rSVI), which combines data on marital status, ethnicity, education, income, employment, psychiatric and somatic comorbidity. The rSVI ranges from 0-14—scores ≥5 defines socially vulnerability. AET was provided free-of-charge at six-monthly follow-up visits after diagnosis and registered in the Danish Breast Cancer Group's treatment database. We defined two AET adherence measures: 1) adherence patterns over five years using group-based trajectory modelling and 2) early discontinuation, i.e., stopping >6 months before end of follow-up. We estimated the associations of social vulnerability with AET adherence patterns and early discontinuation using multinomial and logistic regression, adjusting for age as specified in a directed acyclic graph. To assess the shape of the association between the continuous rSVI score and the adherence measures, we used restricted cubic splines.

Results: Among 4,279 women, we classified 10% as socially vulnerable. The median rSVI score was 5.5 in socially vulnerable women and 1.5 in the remaining cohort. We identified three AET adherence patterns—high adherence (57%), slow decline (36%), and rapid decline (6.9%); 17% discontinued early. Socially vulnerable women had lower AET adherence than the remaining cohort. The odds ratios (OR) and 95% confidence intervals were 1.29 (1.04, 1.60) and 2.38 (1.72, 3.30) for slow and rapid decline, both compared with high adherence. For early discontinuation the OR was 1.77 (1.40, 2.24). The splines suggested positive, linear associations of the continuous rSVI score with adherence patterns and early discontinuation.

Conclusions: Socially vulnerable women have a risk of low AET adherence. Our results may inform the development of targeted interventions to increase AET adherence.