In preclinical models of HER2+ BC, modulation of the intestinal microbiota by antibiotics decreased the antigen processing and presentation pathways at the ileum level and diminished the inflammatory response and type I IFN pathway, preventing commensal bacteria from instructing mononuclear phagocytes, such as DCs, to maintain the proper immune tone in the steady state. The gene discussed is ERBB2; the disease is breast cancer.