Preventing High Blood Sugar in People Being Treated for Metastatic Breast Cancer

Inclusion Criteria: * Histologically confirmed metastatic HR-positive, HER2-negative breast cancer. HR positive is defined by ER status \>10% immunohistochemical (IHC) staining of any intensity. HER2 negativity is defined as the following as per the 2018 American Society of Clinical Oncology and College of American Pathologists guidelines: * IHC score of 0 or 1+ or * Single-probe average HER2 copy number of \<4 signals/cell or * Dual-probe HER2/CEP17 ratio \<2 with an average HER2 copy number of \<4 signals/cell or * IHC 0, 1+, or 2+ and dual-probe HER2/CEP17 ratio ≥2 with an average HER2 copy number of \<4 signals/cell or * IHC 0 or 1+ and dual-probe HER2/CEP17 ratio \<2 with an average HER2 copy number of ≥6 signals/cell or * IHC 0 or 1+ and dual-probe HER2/CEP17 ratio \<2 with an average HER2 copy number of ≥4 and \<6 signals/cell. * Presence of one or more activating PIK3CA mutations in tumor tissue. * Measurable or non-measurable disease per RECIST v1.1 OR at least one predominantly lytic bone lesion must be present. * Written informed consent provided * Female or male ≥18 years of age * Adequate archived tumor tissue for the analysis of PIK3CA mutational status or evaluable circulating tumor DNA (ctDNA) for analysis of PIK3CA mutation status * Recurrence or progression of disease during or after endocrine-based therapy * Eastern Cooperative Oncology Group performance status of 0 or 1. * Life expectancy ≥6 months. * Adequate organ and marrow functio…