PECAM1 and biliary tract neoplasm: Multiplex immunohistochemical (mIHC) staining revealed that in non‐responding biliary tract cancer (BTC) tissues treated with targeted and immune combination therapy, there was an increase in ADM and CD31 expression, a decrease in VE‐cadherin levels, an increase in vascular density and disrupted vascular morphology (Figures S4A and S4B).