TPH1 and familial pancreatic carcinoma: The current study demonstrated an additional important role of 5-HT7 in inducing drug resistance and CSCs in pancreatic cancer by elucidating the mechanism regulating 5-HT7 expression: that is, inhibition of 5-HT7 by its antagonist or removal of 5-HT via TPH1 inhibition suppressed 5-HT7 expression in PANC-1 and MIA PaCa-2 cells.