Oral Aromatase Inhibitors Modify the Gut Microbiome

This study investigates how aromatase inhibitors — a common hormone-blocking pill used to treat breast cancer — affect the bacteria living in a patient's gut (the gut microbiome). Understanding these changes could help explain side effects and lead to better management strategies. **You may be eligible if...** - You are 18 or older - You have been diagnosed with in situ or invasive breast cancer - Your doctor is recommending you start aromatase inhibitor therapy - You are able to read, understand, and sign the consent form **You may NOT be eligible if...** - You have taken antibiotics within the past 4 weeks - You received chemotherapy within the past 4 weeks - You are currently on hormone replacement therapy or anti-estrogen therapy - You are a male with breast cancer - You have a serious unstable medical or psychiatric condition Talk to your doctor to see if this trial is right for you.