Potentially Modifiable Factors Associated with Adherence to Adjuvant Endocrine Therapy among Breast Cancer Survivors: A Systematic Review

SIMPLE SUMMARY: Endocrine therapy taken after primary breast cancer treatment helps prevent breast cancer recurrence. However, many women are unable to adhere to endocrine therapy. This review examines potentially modifiable factors that are associated with endocrine therapy adherence, which might help future efforts to improve endocrine therapy use. Six categories of factors were identified: side effects, attitudes toward endocrine therapy, psychological factors, healthcare provider-related factors, sociocultural factors, and general or quality of life factors. Overall, self-efficacy (i.e., one’s belief in their ability to do something) and positive decisional balance (i.e., one’s belief that the benefits of endocrine therapy outweigh the risks) were the most consistently associated with adherence. They might represent factors worth investigating in future studies seeking to support the adherence of breast cancer survivors. ABSTRACT: Adjuvant endocrine therapy (AET) reduces risk of breast cancer recurrence. However, suboptimal adherence and persistence to AET remain important clinical issues. Understanding factors associated with adherence may help inform efforts to improve use of AET as prescribed. The present systematic review examined potentially modifiable factors associated with adherence to AET in accordance with PRISMA guidelines (PROSPERO registration ID: CRD42019124200). All studies were included, whether factors were significantly associated with adherence or results were null. This review also accounted for the frequency with which a potentially modifiable factor was examined and whether univariate or multivariate models were used. This review also examined whether methodological or sample characteristics were associated with the likelihood of a factor being associated with AET adherence. A total of 68 articles were included. Potentially modifiable factors were grouped into six categories: side effects, attitudes toward AET, psychological factors, healthcare provider-related factors, sociocultural factors, and general/quality of life factors. Side effects were less likely to be associated with adherence in studies with retrospective or cross-sectional than prospective designs. Self-efficacy (psychological factor) and positive decisional balance (attitude toward AET) were the only potentially modifiable factors examined ≥10 times and associated with adherence or persistence ≥75% of the time in both univariate and multivariate models. Self-efficacy and decisional balance (i.e., weight of pros vs. cons) were the potentially modifiable factors most consistently associated with adherence, and hence may be worth focusing on as targets for interventions to improve AET adherence among breast cancer survivors.