On the other hand, the positive correlations between HHLA2 expression and serum CEA, CA19–9 levels, two tumor biomarkers that generally reflect tumor burden both at primary sites and in the circulation for ICC, indicating that patients with HHLA2 overexpression are more likely to suffer from recurrence and metastasis [29]. Here, HHLA2 is linked to intrahepatic cholangiocarcinoma.