Oral Aromatase Inhibitors Modify the Gut Microbiome

Inclusion Criteria:

Pathologic diagnosis of invasive breast cancer ER+ and/or PR+ by IHC (>10% staining), HER2 negative
Postmenopausal women diagnosed with ER+/PR+ invasive breast cancer (unilateral, bilateral, multifocal disease will be eligible provided that all invasive cancers are ER and/or PR +)
Menopause defined as cessation of menstrual cycle for 12 months or determined by follicle-stimulation hormone (FSH) of >40 mlU/mLand estradiol levels of <30 pg/mL level.
No history of breast cancer (DCIS or invasive breast cancer) in either breast prior to the current breast cancer diagnosis
ECOG performance status 0,1,or 2
Completed surgery and planned completion of radiation therapy before initiating aromatase inhibitor
Recommended aromatase inhibitor for systemic treatment of breast cancer
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.
Have HER2 amplified breast cancer
Have triple negative breast cancer
Administered chemotherapy < 4 weeks prior to endocrine therapy initiation
Prior endocrine therapy
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