Gene expression data indicated that 93% (54 of 58) of HER2 gene probes showed reduced HER2 gene expression in both TDM1R and TDXdR BC cell lines compared to in parent cell lines (Fig. 3C), and we confirmed that the alternative splicing index of ERBB2, MIEN1, MIR4728, and PGAP3 genes was significantly increased in both types of TDM1R and TDXdR BC cell lines, resulting in mRNA reduction (Fig. 3D). Here, MIR4728 is linked to breast cancer.