INS and neoplasm: Immunostaining for ATP6AP2 and insulin in different types of NET demonstrated that ATP6AP2 proteins were clearly detected in normal islets and tumor cells in G1 NET, but not in G2/G3 NET cells (Fig. S3), which suggests that the expression level of ATP6AP2 is likely to be correlated with proliferation capacity of NET cells, and can be a therapeutic target in certain types of NETs.