Objectives: The aim of the present study is to assess the significance of metabolomics and genetics in diagnosing and survival evaluation for pNET in the periodic follow-up of MEN1 patients. Aim 1: To evaluate the relationship of serum global metabolic profiles with subsequent development of aggressive PNET and evaluate patients survival in a nested case-control study of MEN1 patients who have developed aggressive PNETs (cases) and MEN1 patients who have developed non-aggressive PNETs (controls). Aim 2: Validate the top serum metabolites identified from Aim 1 in MEN1 patients who have developed aggressive PNETs and MEN1 patients who have developed non-aggressive PNETs, using a targeted metabolomics approach. Aim 3: Prospectively identify the potential miRNA biomarkers of serum with miRNA sequencing in MEN1 patients who have developed aggressive PNETs (cases) and MEN1 patients who have developed non-aggressive PNETs (controls). Aim 4: Validate the potential miRNA biomarkers identified from Aim 1 in MEN1 patients who have developed aggressive PNETs and in MEN1 patients who have developed non-aggressive PNETs, using a targeted qRT-PCR approach (in serums), as well as to see the relationship of potential miRNA biomarkers with patients survival.