RET and cancer: Both in vitro and in vivo studies have demonstrated that abnormal FGF/FGFR signaling may be associated with the occurrence and development of breast tumors.[53] Moreover, overexpression and/or abnormal activation of FGFRs are often related to acquired resistance to established cancer therapies.[54] A variety of therapeutic approaches targeting the FGF/FGFR signaling pathway have recently been developed.[55,56] Lenvatinib (E7080), a small molecule targeting FGFR1-4, VEGFR1, PDGFR, RET, and KIT, has been shown to inhibit lymph node and lung metastasis in BC xenograft models.[57]