ICC has been recently classified into three groups, pure mucin-producing ICC (muc-ICC), predominant mucin-producing ICC with hepatocytic differentiation areas and/or ductular areas in the tumor (mixed-ICC), and predominant ductular areas with hepatocytic differentiation areas with muc-producing ICC areas (cholangiolocellular carcinoma; CLC)41. The gene discussed is MUC5AC; the disease is neoplasm.