MMP9 and cancer: From the results of bioinformatics analysis of differences in proteins between high and low neuroticism, we 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.