Banerjee et al. conducted a comprehensive microbial profiling analysis and identified bacterial signatures that were specific to breast cancer subtypes: HR+/HER2– tumors were associated with Arcanobacterium, Bifidobacterium, Cardiobacterium, Citrobacter, and Escherichia, many of which are known gut or mucosal commensals; HR–/HER2+ tumors were predominantly associated with Streptococcus, a genus that includes both commensal and pathogenic species, some of which have been implicated in inflammatory processes [31]. Here, ERBB2 is linked to breast cancer.