Previous studies have reported that patients with metastatic insulinomas have elevated proinsulin levels (>1000 pmol/L) and a high proinsulin/insulin molar ratio (>3), while non-metastatic insulinomas always present proinsulin levels <200 pmol/L and proinsulin/insulin molar ratio of nearly 1 (8, 23). This evidence concerns the gene INS and pancreatic insulinoma.