SOX9 and cancer: Intriguingly, there were many cancer-related genes that could be novel downstream targets of SOX2 (for example, LTF, PPP2R1B, TGFBR2, SERPINE1, MMP9, HMGA1, SOX9 and PLAC1), and squamous cell differentiation markers KRT6E and KRT6C, whose amino acid sequences are highly conserved among the KRT6 family members and virtually identical to one of the known SOX2 downstream genes, KRT6A (Table 2 and Table S1) [17].