Supporting endocrine therapy adherence in women with breast cancer: findings from the ROSETA pilot fractional factorial randomized trial

Adherence to adjuvant endocrine therapy (AET) in women with breast cancer is poor. Multicomponent intervention packages are needed to address adherence barriers. Optimizing these packages prior to definitive evaluation can increase their effectiveness, affordability, scalability, and efficiency. To pilot procedures for an optimization-randomized controlled trial (O-RCT) of the 'Refining and Optimizing Strategies to support Endocrine Therapy Adherence' (ROSETA) intervention. This was a multisite individually randomized external pilot trial using a 24-1 fractional factorial design (ISRCTN10487576). Breast cancer survivors prescribed AET were recruited from 5 hospitals and randomized to one of 8 conditions, each comprising a combination of 4 intervention components set to "on" or "off" (SMS messages, information leaflet, guided self-help, and self-management website). We set criteria to inform the decision to progress to an O-RCT for consent rate, component adherence, and availability of outcome measures, with predefined cutoffs for "green" (proceed), "amber" (minor changes), and "red" (major changes). Among 141 eligible patients, 54 (38.3%) consented (green range). At least 50.0% of participants adhered to the minimum threshold set for each intervention component (green range). Data for one of the 3 medication adherence measures were available (amber range). Most (86.8%) participants were satisfied with their trial experience. Exploratory analysis indicated some evidence of a negative main effect of the information leaflet on medication adherence (adjusted mean difference = 0.088, 95% CI, 0.018, 0.158). Progression to a fully powered O-RCT of the ROSETA intervention package is feasible, but review of medication adherence measures is required.