LGR4 and cancer: LGR4 plays critical roles in cell proliferation and migration during organ development [11,13,14,15,16,17], whereas LGR5 is specifically expressed in adult stem cells in the gastrointestinal (GI) tract and upregulated in GI cancers [18], and LGR5-positive cancer cells act like cancer stem cells that fuel the growth of tumor mass and metastasis [19,20].