Identifying Determinants of Adherence to Adjuvant Endocrine Therapy Following Breast Cancer: A Systematic Review of Reviews

Background: In oestrogen-receptor positive breast cancer, daily oral adjuvant endocrine therapy (ET) for at least 5 years significantly reduces risks of recurrence and breast cancer-specific mortality. However, many women are poorly adherent to ET. Development of effective adherence support requires comprehensive understanding of influences on adherence. We undertook an umbrella review to identify determinants of ET adherence.

Methods: We searched PubMed, Embase, CINAHL, PsycINFO, Cochrane and PROSPERO (inception to 08/2022) to identify systematic reviews on factors influencing ET adherence. Abstracted determinants were mapped to the World Health Organization's dimensions of adherence. Reviews were quality appraised and overlap assessed.

Results: Of 5732 citations screened, 17 reviews were eligible (9 quantitative primary studies; 4 qualitative primary studies; 4 qualitative or quantitative studies) including 215 primary papers. All five WHO dimensions influenced ET non-adherence: The most consistently identified non-adherence determinants were patient-related factors (e.g. lower perceived ET necessity, more treatment concerns, perceptions of ET 'cons' vs. 'pros'). Healthcare system/healthcare professional-related factors (e.g. perceived lower quality health professional interaction/relationship) were also important and, to a somewhat lesser extent, socio-economic factors (e.g. lower levels of social/economic/material support). Evidence was more mixed for medication-related and condition-related factors, but several may be relevant (e.g. experiencing side-effects, cost). Potentially modifiable factors are more influential than non-modifiable/fixed factors (e.g. patient characteristics).

Conclusions: The evidence-base on ET adherence determinants is extensive. Future empirical studies should focus on less well-researched areas and settings. The determinants themselves are numerous and complex in indicating that adherence support should be multifaceted, addressing multiple determinants.