Although systemic treatment for early stage HER2-positive breast cancer is becoming increasingly effective, resistance and side effects of current treatment modalities are substantial. There is an urgent need for novel therapies, and in addition, better predictive tools are needed to select the right drug to the right patient. New data suggest that modulation of the microbiome of the gut might provide opportunities to increase anti-tumor efficacy of cancer therapies.~A better understanding of the composition, function and dynamics of the gut microbiome before and during trastuzumab-containing neoadjuvant treatment might help to identify factors that can be influenced during the treatment of patients with primary HER2-positive BC .~This study will prospectively enroll 100 participants with newly diagnosed HER2-positive breast cancer patients undergoing standard of care trastuzumab-containing neoadjuvant treatment and correlate gut microbiome composition with pCR.~Patients will be treated with the standard of care neoadjuvant therapy. Stool and peripheral blood (PB) samples will be collected at time of consent for therapy, mid-treatment, after the completion of neoadjuvant treatment (at the discretion of the medical oncologist). Correlation of changes in gut microbiome and metabolic changes, as well as inflammation and microbiome metabolites, will be assessed and possible connection with pCR and side effects will be explored.
In this study the characteristics and alterations of the gut microbiome during neoadjuvant therapy for HER2-positive breast cancer patients are studied, as well as the relation between the gut microbiome and probability of pCR.