The putative stem cell phenotype (CD44+/CD24− and/or ALDH1+/CD24−) has been detected in CTCs [20], and the tumor microenvironment regulates the plasticity of cancer stem cells through transition between epithelial to mesenchymal-like (EMT) and mesenchymal to epithelial-like (MET) states [21]. This evidence concerns the gene ALDH1A1 and neoplasm.