Furthermore, in 31–58% of patients with sporadic gastrinomas [457,458] without a germline MEN1 mutation present, there is an MEN1 gene mutation in the gastrinomas, which is a similar situation in other sporadic non-gastrinoma pNETS which can have MEN1 mutation only in the pNET in 20–40% [459,460,461]. Here, MEN1 is linked to gastrin-producing neuroendocrine tumor.