We utilized a syngeneic mouse metastatic breast cancer model instead of conventional xenografts in immunocompromised nude mice that more accurately mimics human breast cancer.35, 36 ERα-negative 4T1 cells were orthotopically implanted into the second mammary fat pad of immunocompetent mice and randomized to insure similar tumor burdens before treatment. The gene discussed is ESR1; the disease is breast carcinoma.