PURPOSE Adjuvant endocrine therapy (AET) is a life-saving medication for patients with hormone-sensitive breast cancer, yet many struggle with adherence, warranting behavioral intervention. In our recent trial, participation in a group cognitive behavioral intervention (STRIDE) for symptom management and adherence was associated with improvements in symptom distress, coping, quality of life, and mood. We now explore whether baseline patient- and medication-specific factors—which may be modifiable by clinician-led discussions—moderated the effect of STRIDE on adherence rates. METHODS From October 2019 to June 2021, 100 patients with early-stage breast cancer reporting AET-related distress were enrolled and randomly assigned to STRIDE or a medication monitoring (MM) control group. All patients stored their AET in electronic pill bottles to track objective adherence. Patients also self-reported their adherence on the Medication Adherence Report Scale-5 and their perceptions of AET on the Cancer Therapy Satisfaction Questionnaire at baseline. We conducted hierarchical linear modeling to test moderators of intervention effects on objective adherence rates. We report the time × group × moderator effects. RESULTS Among patients reporting greater perceived difficulties with AET adherence at baseline, STRIDE participants had higher adherence rates over time compared with MM ( b = –13.80; SE = 4.56; P < .01). Patients with greater expectations of therapeutic benefit from AET also had improved adherence rates if they were assigned to STRIDE, versus MM ( b = 0.25; SE = 0.10; P = .01). Patients who perceived taking AET as convenient and had been taking their AET for less time had higher adherence rates in STRIDE, versus MM. CONCLUSION The current study identified patient- and medication-specific factors that may augment AET adherence interventions and may be modifiable through clinician-led discussions, such as perceptions of adherence problems, therapeutic efficacy, and convenience of AET.
