In breast cancer (BC), chemotherapy‐induced secretion of miR‐378a‐3p and miR‐378d in exosomes is significantly upregulated and acts on adjacent BC cells, silencing Dickkopf 3 and NUMB and activating the stemness pathways of WNT and NOTCH, allowing BC to become chemoresistant.109. Here, DKK3 is linked to breast cancer.