The ambiguous sensitivity of MUC5AC for BTC in tissue samples can be inferred from the numerous BTC tissue studies mentioned earlier, where the percentage of MUC5AC-positive tumors for CCA and GBC was highly variable, ranging from 8% to 100% (CCA) and 16.67% to 90% (GBC), depending on tumor subtype and MUC5AC antibodies (see Table 1). Here, MUC5AC is linked to cholangiocarcinoma.