The results revealed that (Figure 5C) relative to the NC group, the positive rate of Ki‐67 increased in the NC group; increased in the CCAT2 group; and decreased in the si‐CCAT2, CCI‐779, and CCAT2 + CCI‐779 groups versus the NC group, suggesting overexpression of CCAT2 in vivo could improve the drug resistance of 5‐Fu in BC‐resistant transplanted tumours. The gene discussed is CCAT2; the disease is breast cancer.