Tirzepatide for Weight Loss in Early Breast Cancer

Inclusion Criteria: 1. Female or male patients ≥18 years of age 2. Have a diagnosis of node-positive, hormone receptor-positive (ER+ \> 10%), and HER2-negative breast cancer within the past 15 years per the American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines 1. If patients have synchronous bilateral ER+ breast cancers, tissue from both primary cancers should be submitted for next-generation sequencing (NGS) to inform ctDNA testing 2. Patients with multifocal/multicentric cancers are eligible and the largest focus of cancer should be submitted for NGS evaluation. If tested, all tumor foci must meet have ER \> 10% 3. For patients who received neoadjuvant therapy and have discordant hormone receptor and/or HER2 results between the diagnostic biopsy (pre-treatment) and the surgical pathology (post-neoadjuvant treatment), the hormone receptor status and HER2 status of the post-treatment specimen will determine eligibility 3. Overweight or obesity defined as body mass index (BMI) \> 27 kg/m2 4. Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0-1 5. Have received at least 1 year of or having completed standard neo/adjuvant endocrine therapy. If adjuvant cyclin dependent kinase (CDK) 4/6 inhibitor therapy was prescribed, patients must have completed this therapy 6. Positive ctDNA blood test as determined by the Haystack Oncology Haystack MRD tumor-informed ctDNA assay 7. Patients must have formalin-fixed paraffin-embedded (FFPE) tissue from the primary tumor available for submission to Haystack Oncology to perform whole genome sequencing (WGS) to build customized mutation panel to monitor for plasma ctDNA 8. No clinical evidence of metastatic breast cancer found on history, physical examination, complete blood count (CBC), comprehensive metabolic panel (CMP), and radiologic imaging following a finding of positive ctDNA 9. Have adequate hematologic function, defined by: 1. Absolute neutrophil count (ANC) \>1500/µL 2. Platelet count ≥100,000/ µL 3. Hemoglobin ≥9 g/dL or ≥5.6 mmol/L 10. Have adequate liver function, defined by: 1. Aspartate aminotransferase (AST) and alanine transaminase (ALT) ≤3 x the upper limit of normal (ULN) 2. Total bilirubin ≤1.5 x ULN OR direct bilirubin ≤ULN for patients with total bilirubin levels \>1.5 × ULN 11. Have adequate renal function, defined by: a. Serum creatinine ≤1.5 x ULN or calculated creatinine clearance of ≥30 mL/min 12. Patients must be accessible for treatment and follow-up 13. All patients must be able to understand the investigational nature of the study and give written informed consent prior to study entry Exclusion Criteria: 1. Prior bariatric surgery and/or endoscopic procedures for weight loss (e.g., intragastric balloon, sleeve gastrostomy) following diagnosis of breast cancer 2. Treatment with a GLP-1/Glucagon receptor agonist, GIP/GLP-1/Glucagon receptor agonist, GIP/GLP receptor agonist, or any combinations with GLP-1 receptor agonist therapies within the last 3 months 3. History of severe hypersensitivity reaction to GLP-1/Glucagon receptor agonist, GIP/GLP-1/Glucagon receptor agonist, or any combinations with GLP-1 receptor agonist therapies 4. Insulin-dependent diabetes 5. Has clinical evidence of diabetic retinopathy 6. Clinical evidence or suspicion of metastatic breast cancer 7. Current or past invasive cancers, other than breast cancer, are not allowed except for: 1. Adequately treated basal or squamous cell carcinoma of the skin 2. Previously diagnosed invasive cancer treated with curative intent, with no evidence of disease recurrence for at least 5 years, and are considered low risk for future recurrence by the treating physician 8. Patients with a second synchronous primary HER2-positive or triple negative breast cancer 9. Has an active infection requiring systemic therapy 10. Has a known history of human immunodeficiency virus (HIV) or active or persistent hepatitis B or hepatitis C virus 11. Has significant cardiovascular disease, such as: 1. History of stroke, myocardial infarction, acute coronary syndrome, or coronary angioplasty/stenting/bypass grafting within the last 6 months 2. Congestive heart failure (CHF) New York Heart Association (NYHA) Class II-IV, or history of CHF NYHA class III or IV. 12. Has a known history of active tuberculosis 13. Women who are pregnant or lactating. All patients of reproductive potential must agree to use effective contraception from time of study entry until at least 3 months after the last administration of study drug 14. Patients who have any severe and/or uncontrolled medical conditions or other conditions that could affect their participation such as: 1. severe impaired lung functions as defined as spirometry and diffusing capacity of lung for carbon monoxide (DLCO) that is 50% of the normal predicted value and/or O2 saturation that is 88% or less at rest on room air 2. liver disease such as cirrhosis or severe hepatic impairment (Child-Pugh class C) 3. history of gastroparesis, impaired gastrointestinal (GI) function, or GI disease that may significantly alter the absorption of the study drug (e.g., ulcerative diseases, uncontrolled nausea vomiting and/or diarrhea, malabsorption syndrome, or small bowel resection) 15. Has a history of pancreatitis or current symptoms of untreated cholelithiasis 16. Has a family history of Multiple Endocrine Neoplasia Syndrome Type 2 (MEN 2) or medullary thyroid cancer (MTC) 17. Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the study, interfere with the patient's full participation for the full duration of the study, or results in trial participation not being in the patient's best interest, in the opinion of the Treating Physician 18. Has received an investigational agent within 4 weeks prior to study treatment; investigational monoclonal antibodies should have a 4-week (28 day) or 5 half-life washout period 19. Any other investigational or anti-cancer treatments while participating in this study with the exception of standard adjuvant endocrine therapy, zoledronic acid, or denosumab