Racial Differences in Symptom Burden and Endocrine Therapy Adherence in Breast Cancer: A Post Hoc Analysis of a Randomized Trial

Background: Adjuvant endocrine therapy (AET) reduces the risk of breast cancer recurrence, but racial differences in nonadherence persist, potentially reflecting variations in symptom burden. We conducted a post hoc analysis of the THRIVE trial to investigate symptom burden and AET adherence by race among women with early-stage breast cancer. Patients and Methods: We included Black and White women who enrolled in the THRIVE trial, a remote monitoring intervention, from November 2018 to June 2021. Participants completed surveys at baseline and at months 6 and 12, including symptom burden measured using the Functional Assessment of Cancer Therapy-Endocrine Subscale (FACT-ES) instrument. Adherence was defined as the proportion of days covered >80% using an electronically monitored pillbox. Multivariable regression analyses were performed to examine factors associated with adherence, and Kitagawa-Oaxaca-Blinder decomposition was used to quantify the proportion of adherence differences explained by symptom and patient characteristics. Results: Among 102 (34.7%) Black and 192 (65.3%) White women randomized to 3 study arms evaluating the efficacy of the remote monitoring intervention, 84% completed the 6-month survey, and 87% completed the 12-month survey. Black participants were younger and had lower income and health literacy ( P <.01). Black women reported worse symptoms at baseline (60.9 vs 64.4; P =.003) and month 12 (57.0 vs 61.9; P <.001), yet a similar proportion experienced 5-point decreases (the minimally important difference) over the 12-month period (34.9% vs 32.4%; P =.69), compared with White women. At month 12, fewer Black participants were adherent to AET than White participants (43.0% vs 60%; difference=17.0 percentage points ppts; P =.009). This difference was attenuated after adjusting for symptoms and patient characteristics (−7.75 ppts; P =.34). Baseline symptoms (0.77 ppts; P =.021) were significantly associated with adherence over 12 months, whereas changes in symptoms were not (0.14 ppts; P =.69). Symptom and patient characteristics together accounted for 58% of the 1-year adherence difference between racial groups. Conclusions: Black women had lower 1-year AET adherence compared with White women, largely attributed to baseline symptoms and sociodemographic characteristics. More proactive symptom management and addressing social determinants of health among Black women may alleviate disparities in AET adherence. ClinicalTrials.gov Identifier: NCT03592771