As shown in Figure 1A, the viable curve of T47D cancer cells is extremely similar with that of MCF‐7 cells, but distinctly different with that of MDA‐MB‐231 and MDA‐MB‐435 cells, as well as the IC50, indicating that the breast cancer cells with expression of ERα is more sensitive to CPT than those without expression of ERα. The gene discussed is ESR1; the disease is cancer.