Kim et al. recently reported that expression of YAP, CTGF, and CYR61 is elevated in recurrent breast cancer tissues after tamoxifen treatment; they also showed that YAP overexpression leads to tamoxifen-resistance and downregulation of ERα (Kim et al., 2021), as is consonant with the notion that expression of ERα is decreased in TNBC cell lines. This evidence concerns the gene CCN1 and breast cancer.