In addition, fisetin conjugated with cationic triphenylphosphonium groups (mito-fisetin mF3, 4) exhibited a much more potent antitumor effect in both the in vitro (against hormone-dependent breast cancer cell lines (HCC1500, CAMA-1, HCC1428, and ZR-75-30 cell lines) with tamoxifen-induced senescence) and the in vivo ER-positive breast cancer cell line-based xenograft system [179]. This evidence concerns the gene ESR1 and breast cancer.