The goal of this clinical trial is to evaluate whether oral creatine supplementation can prevent chemotherapy-related cognitive impairment in patients with early-stage breast cancer undergoing neoadjuvant or adjuvant chemotherapy. The main questions it aims to answer are:
* Does creatine supplementation reduce the occurrence and severity of chemotherapy-related cognitive impairment, as measured by patient-reported cognitive function?
* Does creatine supplementation preserve objective cognitive performance compared with placebo during and after chemotherapy?
Researchers will compare creatine supplementation (5 g/day) with placebo to assess differences in cognitive outcomes, safety, and exploratory biological markers.
Participants will:
* Receive oral creatine or placebo starting 7 days before chemotherapy and continuing until 12 months after chemotherapy completion
* Complete patient-reported cognitive assessments and objective neuropsychological tests at predefined time points
* Undergo clinical follow-up for safety and oncologic outcomes
* Provide blood samples for biomarker analyses and stool samples for gut microbiota assessment
* Undergo brain magnetic resonance imaging at selected study visits