NGF and cholangiocarcinoma: In cholangiocarcinoma (CCA) patients from Caucasian regions, NGF and TrkA are rarely detected in malignant epithelial cells, even though PNI is a classical route of metastasis for CCA, highlighting the potential role of other cell types in the microenvironment (Westphalen et al. 2019; Qian et al. 2024).