Oral Aromatase Inhibitors Modify the Gut Microbiome

Primary Objective: To describe the microbiome shift of gut microbiome from baseline after 4-weeks and 12-weeks of oral aromatase inhibitor treatment.

Secondary Objective

• To correlate gut microbiome populations with circulating sex hormone metabolite concentrations at baseline and 12 weeks.
• To describe the correlation of change in the microbiome populations with change in circulating sex hormone metabolite concentrations from baseline to 12 weeks.

Inclusion 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.

Exclusion criteria

• 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