Chronic antibiotics reduced tumor burden, significantly more so in females, and resulted in complete inversion of the sex-biased tumor phenotype: microbiota-depleted ApcMin/+Ret+/− females had significantly fewer tumors than males (3.7 ± 1.5 vs 12.7 ± 1.5, p=0.005, two-tailed Student’s t-test; Figure 3A). The gene discussed is RET; the disease is neoplasm.