Bacteroides ovatus showed a suggestive causal association with BCR (OR = 1.12, 95%CI = 1.01 ~ 1.23, P = 0.03), BC (OR = 1.12, 95%CI = 1.01 ~ 1.25, P = 0.04), and BR (OR = 1.17, 95%CI = 1.02 ~ 1.35, P = 0.03). Here, BCR is linked to breast cancer.