Apart from inducing the transdifferentiation of tumor cells into CSCs and thereupon to ECs during angiogenesis in vivo, hypoxia, which can be created in vitro by reducing oxygen concentration to 1%, was found to enable the cells of several CD31– carcinoma cell lines to transdifferentiate into CD31+ TECs and form tubular vessel-like structures in a 3D cell culture [130,131]. This evidence concerns the gene PECAM1 and carcinoma.