Fig. 2

T test analysis and the VIP score plots of PLS-DA of samples of tumor tissue and 5 cm from tumor (normal tissue). a T test analysis in positive ion mode. b T test analysis in negative ion mode. The vertical coordinate is the P value, the horizontal coordinate is the level of each metabolite, and purple represents the significant metabolites with P < 0.05. c The VIP score plots of PLS-DA in positive ion mode. d The VIP score plots of PLS-DA in negative ion mode. The vertical coordinate represents the M/Z of each metabolite, and the horizontal coordinate is the weight value of each metabolite. It can be seen from the score plot that there are 31 metabolites in the positive ion mode and 40 in the negative ion mode. PLS-DA: partial least squares discriminant analysis. M/Z: mass-to-charge ratio. VIP: Variable Importance in the Projection