Three Antidiarrheal Strategies in HER2+/HR+ Early Breast Cancer Patients Treated With Extended Adjuvant Neratinib

This is an international, multicenter, prospective, controlled, randomized, adaptative, phase II study to evaluate the incidence of discontinuations due to diarrhoea within the first 3 cycles in patients with early-stage HER2+ and HR+ breast cancer treated with neratinib plus loperamide prophylaxis for the first 2 cycles versus neratinib with initial 2-week dose escalation plus PRN loperamide versus neratinib and loperamide plus colesevelam prophylaxis for 28 days. After the preplanned therapy, prophylaxis or treatment for diarrhoea will be given as clinically indicated following the standard of care by the treating physician. Approximately 315 patients will be enrolled in the study. All enrolled patients will receive neratinib orally once daily for 13 cycles, continuously. Eligible patients will be randomly assigned in a 1:1:1 ratio to one of the diarrhoea prophylaxis arms, using an interactive response technology (IRT) module within the electronic data capture (EDC) system. Patients will be stratified according to menopausal status (premenopausal versus postmenopausal) and prior anti-HER2 therapy (trastuzumab only versus trastuzumab plus pertuzumab). Baseline assessments will be performed prior to C1D1 dosing. During the first 3 cycles of treatment, safety data will be collected during the cycle visits. After the first 3 cycles, all patients will enter in a follow-up period to complete approximately 1 year of neratinib treatment. During this follow-up period, safety data will be collected every 3 months. An End-of-Treatment (EOT) Visit is planned on cycle 13 day 28 for all treatment arms (unless patient discontinues earlier), followed by a Safety Follow-up Visit (30 +/-5 days after the last dose of neratinib). This will be the core phase of the study. After this safety follow-up visit, long term outcome data will be collected for 5 years to address the exploratory objectives. This will be the extended phase of the study. Archived primary tumor tissue (at baseline) and whole blood samples (at baseline, during the treatment and follow-up period, and at disease relapse) will be collected for the exploratory analyses. Patients are anticipated to participate in the core phase of the study for approximately 1 year to address primary and secondary objectives (28 days for screening, approximately 12 months to complete neratinib treatment, and 30 days for a safety follow-up visit after the last dose of neratinib). Later on patients will continue in the extended phase of the study and will be followed-up for at least 5 years to collect long term outcome data to conduct the exploratory analyses. The approximate duration of the full study is 8 years. The objectives of the study are indicated below: Primary objectives: To evaluate the incidence of neratinib discontinuations due to diarrhoea within the first 3 cycles (1 cycle = 28 days) in patients with early-stage HER2 overexpressed/amplified (HER2+), hormone receptor-positive (HR+) breast cancer who have completed adjuvant trastuzumab-based therapy. Primary End-point: Incidence of neratinib discontinuations due to diarrhoea at the end of 3 cycles of neratinib treatment. Secondary Objectives: * Incidence and time of neratinib discontinuations due to any treatment-emergent adverse event (TEAE). * Diarrhoea due to neratinib: incidence, duration, severity, and treatment interventions. * Incidence of neratinib discontinuation due to any reason. * Incidence of hospitalisations (overall and for diarrhoea). * Incidence of TEAEs and serious adverse events (SAEs) and adverse events of special interest (AESIs, ie, hepatic, cardiac, pulmonary, reproductive and developmental). * Neratinib exposure assessment. * Determine the effect of study treatment on quality of life, as measured by patient reported outcomes, in all treatment arms. Secondary End-points: * Incidence and time to neratinib discontinuations due to any TEAE. * Incidence, cumulative duration and time to first episode of any diarrhoea and grade 3 or higher diarrhoea. * Incidence and time to neratinib discontinuation due to any reason. * Incidence of hospitalisations due to any reason and diarrhoea. * Incidence of TEAEs and SAEs that included AESIs (i.e. hepatic, cardiac, pulmonary, reproductive and developmental). * Incidence of Neratinib dose modifications (reductions and dose holds), and dose intensity. * Systemic therapy-induced diarrhea Assessment Tool (STIDAT), Functional Assessment of Cancer Therapy Questionnaire for Breast Cancer (FACT B) and EuroQol 5 Dimensions 5 Levels (EQ5D-5L) questionnaires. Exploratory Objectives: Evaluate minimal residual disease (MRD) and molecular alterations associated with patient outcome, and/or the development of diarrhoea with neratinib. Exploratory End-points: Correlation of biomarkers data with patient outcome and safety data.