A monoclonal antibody that selectively binds to Leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) is being developed to inhibit growth of cancer stem cells for the treatment of cancers. LGR5 is a protein that is normally expressed on intestinal stem cells, but is over-expressed on tumor-initiating stem cells in most cancers, including colon, breast, liver, lung, pancreatic, ovarian cancers, and other solid tumors. Cancer stem cells are often resistant to chemotherapy or other conventional forms of cancer therapy, and high expression of LGR5 in colon cancer has been associated with tumor recurrence and poor prognosis.