To determine whether knockdown of OPG could directly impact metastasis, distinct from effects related to a primary tumor, we used the chick embryo experimental metastasis model, outlined in Figure4A. In this model, a section of the shell is removed at embryonic day 12 (E1) and tumor cells are introduced by intravenous injection into the chorioallantoic vein (E2). The gene discussed is TNFRSF11B; the disease is neoplasm.