This study aimed to correlate the initial gut microbiota of newly diagnosed HR+ (Hormone Receptor)/HER2- breast cancer patients with their mental health, cognitive function, and QoL at baseline and after 3 months of neoadjuvant chemotherapy.<h4>Materials and methods</h4>This is a prospective, longitudinal, observational, exploratory study. Here, ERBB2 is linked to breast carcinoma.