To systematically investigate the molecular basis for survival after CAP treatment by breast cancer cell lines which are classified into their intrinsic subtypes such as luminal A (ER+PR+/−HER2−), luminal B (ER+PR+/-HER2+), basal-like (ER−PR−HER2−), and HER2-positive (ER−PR−HER2+), we conducted quantitative real time PCR analysis to screen the genes that are differentially expressed after CHCP treatment. The gene discussed is ESR1; the disease is breast cancer.