In PDAC and CCA, this tumor-promoting mechanism is further amplified: tumor cells and CAFs express TPH1 and actively secrete 5-HT, which not only maintains the dedifferentiation and malignant proliferation of epithelial cells, but also accelerates the malignant progression of tumors by activating 5-HTR to recruit and polarize M2-like TAMs. The gene discussed is TPH1; the disease is neoplasm.