Oral Aromatase Inhibitors Modify the Gut Microbiome

Eligibility Criteria

• * Pathologic diagnosis in situ or invasive breast cancer for which initiating aromatase inhibitors therapy is recommended or initiating aromatase inhibitors for risk reduction.
• * ECOG performance status 0,1, 2, 3.
• * Age ≥ 18 years
• * HER2+ breast cancer is allowed if patients are on a monoclonal antibody therapy for which a change is not anticipated while on study (12 weeks) and they have been on the monoclonal antibody therapy for at least 4 weeks.
• * Ability to read, understand and evaluate study materials and willingness to sign a written informed consent document.
• * Have been on antibiotics within 4 weeks of enrollment.
• * Administered chemotherapy less than 4 weeks prior to enrollment.
• * Hormone replacement (defined as only estrogen and/or progesterone replacement) or anti-estrogen therapy within 4 weeks of starting aromatase inhibitors
• * Use of antibody drug conjugate (HER2+ breast cancer)
• * Male breast cancer
• * Any serious and/or unstable pre-existing medical, psychiatric, or other existing condition that would prevent compliance with the trial or consent process