An exploratory mediation analysis on Genus Anaerostipes id.1991, which showed the strongest nominal signals (TTK inhibition on Anaerostipes: uncorrected p = 0.003; Anaerostipes on BC: uncorrected p = 0.025), was performed for hypothesis generation only; no statistically significant mediation was observed.<h4>Conclusion</h4>This study provides robust genetic evidence that TTK inhibition is causally associated with a decreased risk of breast cancer. Here, TTK is linked to breast carcinoma.