Betacellulin (BTC), a member of the epidermal growth factor (EGF) family, was originally isolated from mouse beta cell tumor (betaTC-3) as a growth–promoting factor and is known to be expressed in pancreatic α-cells, β-cells, and duct cells in adult humans (Miyagawa et al., 1999). Here, BTC is linked to pancreatic insulin-producing neuroendocrine tumor.