Although our results, which show that the major function of the RGD domain is to protect cancer cells from stress-induced apoptosis are different from prior studies using recombinant bacterially derived OPN [36], [37], [38], [39], they are consistent with studies which used human-derived soluble OPN or antibodies that block autocrine OPN function [40], [41], [42], [43]. This evidence concerns the gene SPP1 and cancer.