We performed orthotropic metastasis assay by implanting of several breast cancer cell lines with varied lung metastasis capacities into mice fat pads, including the murine cell lines 67NR (low metastatic potential), 4T1 (high metastatic potential) and human cell lines MCF7 (estrogen receptor+ cells, low metastatic potential), MDA-MB-231 (triple-negative cells, high metastatic potential). The gene discussed is ESR1; the disease is breast cancer.