The EAY191-N2 clinical study, Phase II Trial of Fulvestrant and Binimetinib in Patients with Hormone Receptor-Positive Metastatic Breast Cancer with a Frameshift or Nonsense Mutation or Genomic Deletion in NF1, part of the ComboMATCH precision medicine initiative, is open for patients who have hormone receptor-positive (HR+) breast cancer with NF1 Nonsense or Frameshift mutation. Patients will be enrolled into two different cohorts. Cohort 1 is testing the combination of fulvestrant and binimetinib in HR+ patients who have never received fulvestrant (fulvestrant-naïve). Cohort 2 is assessing the addition of binimetinib to fulvestrant for patients who have previously received fulvestrant (fulvestrant-exposed) and their disease progressed.