ESR1 and cancer: Mitochondria are considered as promising targets forcancer treatment.In the present study, triphenyl phosphonium cationic group-conjugatedfisetin (mito-fisetin) was synthesized, and its anticancer activitywas investigated in several cellular models of estrogen receptor (ER)-positivebreast cancer in vitro and in vivo in proliferating and tamoxifen-promotedsenescent states.