Neoadjuvant Neratinib in Stage I-III HER2-Mutated Lobular Breast Cancers

PRIMARY OBJECTIVE: I. Determine efficacy of neoadjuvant neratinib in combination with endocrine therapy. SECONDARY OBJECTIVES: I. Determine additional efficacy outcomes of neoadjuvant neratinib in combination with endocrine therapy. II. Compare the safety and tolerability of neratinib plus endocrine therapy. CORRELATIVE OBJECTIVE: I. Establish HER2-mutant invasive lobular carcinoma (ILC) organoids. OUTLINE: Patients are randomized to 1 of 2 treatments. TREATMENT A: Patients receive standard of care endocrine therapy over 4 weeks for 1 cycle. Patients undergo breast tissue biopsy during the lead-in window/cycle 1. Patients then endocrine therapy and neratinib orally (PO) daily for 20 weeks in the absence of disease progression or unacceptable toxicity. Patients undergo breast surgery during weeks 24-25. Patients undergo collection of blood samples every 4 weeks while on treatment, at weeks 4 and 24, and at time of surgery. Patients undergo mammogram, ultrasound, or breast magnetic resonance imaging (MRI) prior to surgery. TREATMENT B: Patients receive standard of care endocrine therapy and neratinib PO over 4 weeks for 1 cycle. Patients undergo breast tissue biopsy during the lead-in window/cycle 1. Patients then continue endocrine therapy and neratinib PO daily for 20 weeks in the absence of disease progression or unacceptable toxicity. Patients undergo breast surgery during weeks 24-25. Patients undergo collection of blood samples every 4 weeks while on treatment, at weeks 4 and 24, and at time of surgery. Patients undergo mammogram, ultrasound, or breast MRI prior to surgery. After completion of study treatment, patients are followed up for 4 weeks after study drugs interruption.