When MUC5AC and angiopoietin-2 were combined with CA19-9 (Figure 4B,D), the proportions of CCA patients with CA19-9-low levels detected were in 6/12 cases (50%) for MUC5AC ≥ 104.6 ng/mL and 3/12 cases (25%) for angiopoietin-2 ≥ 2422 pg/mL. The gene discussed is MUC5AC; the disease is cholangiocarcinoma.