VEGFR-1 was initially believed to be expressed by only endothelial cells; however, recent studies, including from us, have demonstrated that VEGFR-1 is also expressed on a variety of tumor cells, including colon, breast, gastric, osteosarcoma, pancreatic, melanoma, prostate and ovarian cancers [7,8,9,10,11,12,13,14,15,16,17,18]. Here, FLT1 is linked to osteosarcoma.