Sequencing revealed 1,561 microbial taxa.A significant difference in genus composition of gut microbiota between patients and controls (unweighted UniFrac p = 0.009).Decreased α-diversity of gut microbiota (p ≤ 0.004) at patients than that of controls, except for the Shannon index (p = 0.09).Showed alteration of the composition of their IgA-positive (p = 0.02) and IgA-negative (p = 0.05) intestinal microbiota and significant reduction of α-diversity (p ≤ 0.05) in BC patients after adjusting for estrogens and other factors. Here, CD79A is linked to breast cancer.