Gut and Tumor Microbiome in Patients With Early Stage (II-III), Locally Advanced or Advanced ER-positive and HER2-negative Breast Cancer.

After being informed about the study and potential risks, all participants giving written informed consent will provide a pre-treatment stool sample looking at the gut microbiome, primary tumor sequencing analysis to infer tumor microbiome, and a blood sample for the CyTOF whole blood Immune Profile. Blood tests (full blood count, renal profile, liver profile, C-reactive protein), medical history, concomitant medications, and the Eastern Cooperative Oncology Group (ECOG) performance level will be obtained through a mixture of self-reported and data collated from the electronic health record (EHR). Two food frequency questionnaires will be given to participants to complete at two timepoints: at screening and at end of study. There are 5 study visits. Participants will provide a stool sample for gut microbiome sequencing at weeks 2 and 4 of the study. During the Week 6 visit, participants will provide final stool samples for gut microbiome analysis, and a blood sample for CyTOF whole blood Immune Profile. ECOG performance status and adverse event data will be obtained from EHR.