HTR1D and familial pancreatic carcinoma: HTR1D (5-HT1D), an indispensable member of the serotonergic system, has been demonstrated to play an important role in the regulation of the proliferative and invasive phenotype of pancreatic cancer (PaCa), and downregulation of 5-HT1D receptors inhibits proliferation and invasion of human pancreatic cancer cells [25].