This study will explore whether tirzepatide is a practical and acceptable treatment for postmenopausal females with a history of hormone receptor-positive breast cancer and obesity. The investigators aim to understand whether participants are willing and able to take this medication once weekly for 6 months and whether it may help improve weight and overall health. There will be monthly check-ins to monitor progress and safety. At the beginning and end of the study, participants will undergo body composition assessments, blood tests and a stool sample will be collected, and surveys will be completed.

Inclusion Criteria:

• Biologically female

• Age ≥ 18

• Obesity as defined by current BMI ≥ 30 kg/m²

• Postmenopausal as defined by one or more of the following

  • Age ≥60 years
  • Age <60 years with amenorrhea for ≥ 1 year
  • Documented bilateral surgical oophorectomy
  • Chemical menopause with the addition of LHRH agonists at least 12 weeks prior to enrolment, and plan to remain on LHRH agonists throughout the trial

• HR+ (ER and/or PR) stage 0-III breast cancer

• Completed curative treatment (surgery, chemotherapy, radiotherapy) at least 12 weeks prior to enrolment

• Insurance approval for tirzepatide or willing to pay out of pocket

• Willing to provide informed consent and comply with study procedures

Exclusion Criteria:

• Stage IV breast cancer
• Concomitant use of CDK inhibitors
• Concomitant use of antiHER2 therapy
• The PI may be consulted regarding enrollment of females receiving other endocrine therapy medications
• Other active malignancy requiring treatment
• Enrollment in another investigational clinical trial
• Contraindication to tirzepatide
• Treatment with a GLP-1 receptor agonist within the last 3 months
• Diabetes requiring insulin
• Any disorder, unwillingness, or inability, not covered by any of the other exclusion criteria, which in the investigator's opinion, might jeopardize the subject's safety or compliance with the protocol