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

Inclusion Criteria

• Diagnosed with metastatic HR-positive, HER2-negative breast cancer.
• Cancer must have a specific PIK3CA mutation.
• Must have measurable or non-measurable disease or at least one bone lesion.
• Must provide written informed consent.
• Must be 18 years or older.
• Must have enough tumor tissue or circulating tumor DNA for analysis.
• Cancer must have worsened during or after hormone therapy.
• Must be in good general health with a performance status of 0 or 1.
• Must have a life expectancy of at least 6 months.
• Must have adequate organ and bone marrow function.
• Must have controlled blood sugar levels without needing medications other than metformin.
• Must be able to swallow pills.
• Must be willing to follow any of the diet plans and comply with study requirements.
• Women must be postmenopausal, defined by specific criteria such as age or surgical history.

Exclusion Criteria

• Have had multiple lines of chemotherapy for metastatic cancer (one line is allowed).
• Currently in another study with an investigational drug.
• Currently on a formal weight loss program or ketogenic diet.
• Have a body mass index (BMI) less than 20.
• Have allergies to study drugs or their ingredients.
• Have another active cancer, except for certain skin or cervical cancers.
• Have type 1 diabetes or uncontrolled type 2 diabetes.
• Require certain diabetes medications.
• Follow a vegetarian or vegan diet.
• Have allergies to foods like eggs, gluten, nuts, or milk that would affect diet adherence.
• Have impaired decision-making ability.