Metabolite profiles between different stages of rectal cancer tissues and normal controls. A OPLS-DA scores plots based on each stages of rectal cancer tissues and normal controls; black triangles represent normal controls (n = 43); red diamonds represent stage I (n = 35); blue diamond’s represent stage II (n = 37); green diamonds represent stage III (n = 37); yellow diamonds represent stage IV (n = 18). B Color map showed the significance of metabolite variations between the classes. Peaks in the positive direction indicated the increased metabolites in rectal cancer tissues. Decreased metabolites in rectal cancer tissues were presented as peaks in the negative direction. C Statistical validation of the corresponding PLS-DA models using permutation analysis (200 times). R2 is the explained variance, and Q2 is the predictive ability of the model. D Scores plots of OPLS-DA prediction model. 80% of samples were applied to construct the model, and then used it to predict the remaining 20% of samples.