Functional targets of miR-181b appeared to be relevant for breast cancer and drug resistance and were significantly downregulated in our study, including HEY1, CA2, PIK3R1, LYN, ESR1, JUN, STAT1, MYB, BCL2, CYCS, BAMBI, CTGF and SOX9. MiR-342 was one of the consistently downregulated miRNAs in all resistant cell lines and has been linked with tamoxifen resistance by Cittelly et al. [30] We identified 14 predicted functional targets of miR-342-3p/5p, including FYN, TGFBR1, COL4A6, CDKN1A, and Ephrins EPHA4/7 (Supplementary Figure 2). Here, PIK3R1 is linked to breast cancer.