This anti-metastatic propensity of MB in an animal model nicely extends our previous clinical findings, where the expression of MB in human cases of invasive breast cancer positively correlated with a higher degree of tumor cell differentiation (luminal subtype), progesterone as well as estrogen receptors positivity (ER+), and a significantly better prognostic outcome in ER+ or ER− breast cancer patients3. The gene discussed is ESR1; the disease is breast cancer.