Investigating deprivation-specific and ethnic inequalities in adherence to endocrine therapy in women with ER+ve breast cancer: can these explain disparities in survival?

Background: Breast cancer survival is lower in women from deprived areas and, to a lesser extent, Black women. The reasons for these disparities are unclear, but differential treatment utilisation is a possible explanation.

Although adjuvant endocrine therapy (ET) reduces risks of recurrence and death in women with oestrogen-receptor positive (ER+ve) disease, up to 50% of women have poor adherence to the medication, regularly skipping doses and/or stopping completely before the recommended treatment period. However, contemporary, large-scale, studies of patterns of ET adherence in the UK are lacking.

We will identify if adjuvant ET adherence varies by deprivation and ethnicity and use novel methods to investigate causal pathways linking social characteristics, and adherence and survival.

Aims: To (i) identify whether there are inequalities by deprivation and ethnicity in adjuvant ET adherence, and (ii) determine the extent to which these explain survival disparities.

Methods: A retrospective cohort study will be undertaken using linked CPRD, HES, cancer registration and ONS mortality records.

The cohort will comprise women in England diagnosed with invasive ER+ve breast cancer, Jan 2005-Dec 2019, with at least one ET (tamoxifen/aromatase inhibitor) prescription in 12-months post-surgery.

Using prescription records, a longitudinal daily history of ET availability will be created for each woman, and two measures of adherence computed: persistence (ET continuation/discontinuation) and compliance (cumulative ET availability). Women will be classified by IMD income domain category at breast cancer diagnosis, and ethnic group.

Multiple regression methods will first be used to determine associations between deprivation, ethnicity and adherence.

Patterns of adherence, recurrence and net survival will then be examined and mediation-based survival models used to determine whether adherence mediates relationships between deprivation, ethnicity and survival.

At the end of the project, two PPI workshops will identify key unanswered questions and prioritise ideas for follow-on research and other actions to reduce breast cancer inequalities, with a particular focus on ET adherence.

How the results of this research will be used: The dissemination strategy will ensure findings reach clinical, academic, patient and service-provider/decision-maker audiences. Findings will demonstrate whether there are social inequalities in ET adherence. They will shed light on the “mechanisms” by which deprivation and ethnicity may impact survival in breast cancer.

They will inform the need to target and tailor interventions and clinical services to support ET adherence towards specific social groups. This, in the longer-term, could reduce survival disparities, yielding benefits for patients, the NHS and society.