Wang et al. (2016) reported overexpression of PIWIL4 in breast cancer with a lowered overall patient survival. We observed a similar trend for PIWIL4 expression in CCA. DEP domain containing 1 (DEPDC1) plays a crucial role in tumor growth and metastasis (Huang et al., 2017); a previous study found that the shRNA knockdown of DEPDC1 in glioma cell lines and in mice have better survival (Kikuchi et al., 2017). Patients with high DEPDC1 expression have low survival in CCA (Figure 8). This evidence concerns the gene PIWIL4 and central nervous system cancer.