For example, high levels of cytokeratin-19 (CYFRA 21-1), MMP-7, osteoblasts, periostin, and IL-6 can be detected in the serum of patients with CCA, which may be helpful for further diagnosis of CCA.123–130 In addition to miRNAs, CTCs is an important marker in liquid biopsy of CCA. The gene discussed is KRT19; the disease is cholangiocarcinoma.