SOX9 and cholangiocarcinoma: In HCC, EpCAM is considered as a crucial factor in the maintenance of CSC-like features in cancer cells.24 To investigate whether SOX9 is implicated to the CSC features of CCA cells, we performed tumour sphere formation assay, a widely recognised method to evaluate cancer stem cell self-renewal and differentiation at the single-cell level in vitro.25 SOX9 knockdown significantly inhibited the capacity of tumour sphere formation in CC-SW-1 (Fig. 5d).