TGFB1 and neoplasm: Undoubtedly, the regulation of the CSC pool in vivo before antitumor exposures and, especially, after their application, represents a significantly more sophisticated process than in cells cultured in vitro, as regulation in vivo is subject to the influence of numerous signaling molecules (for example, TGF-b1, FGF, IL-6, HIF, and Wnt ligands) released not only by tumor cells, but also by various stromal cells, including endothelial, immune cells, tumor-associated macrophages, fibroblasts, and normal stem cells [1,22].