The extent of sphere formation is also considered to be correlated with the stem-like cell content of tumor cell populations.24 Acquisition of long-term self-renewal in PAK1 T423E stably transfected cells correlated with a stable upregulation of cancer stem cell (CSC) markers including CD73, CD146,25 and aldehyde dehydrogenase 1 (ALDH1).26 Conversely, the empty vector transfected cells were losing the CSC markers expression along with sphere passaging (Figure 2d and Supplementary Figure 2). This evidence concerns the gene ALDH1A1 and cancer.