iTRAQ was used to identified the characterize differentially expressed proteins between high and low neuroticism, which found that SNCA, ATP7A, GNG2, CDK6, MPO, AZU1, HIST1H2BH, ITGAM and MMP9 might participate in the intrinsic mechanism of neuroticism by regulating response to catecholamine stimulus, catecholamine metabolic process, limbic system development and transcriptional misregulation in cancer pathway. Here, MMP9 is linked to cancer.