Levels of Firmicutes of women associated with early menarche and HER2+ breast cancer were lowest (21.4%), intermediate among women who had later menarche and HER2+ (30.4%) or early menarche and HER2- (50.03%), and highest among those with later menarche and HER2+ (56.24%) 3. This evidence concerns the gene ERBB2 and breast cancer.