PRF1 and cholangiocarcinoma: CCA‐derived exosomes assist CCA cells to escape from immune attack by preventing cytokine‐induced killer (CIK) cells from producing tumour necrosis factor (TNF)‐α and perforin that is critical in the anticancer activities.43 Development and metastasis of CCA is also modulated by CCA‐derived exosomes which can transfer oncogenic proteins, and oncogenic proteins can accelerate tumour progression by inducing β‐catenin and reducing E‐cadherin expressions in CCA cells.44