Fig. 1

TIC chromatograms of metabolites and principal component analysis of samples of tumor tissue and 5 cm from tumor (normal tissue). a TIC profiles of tumor tissue in the positive ion mode; (b) TIC profiles of normal tissue in the positive ion mode. c TIC profiles of tumor tissue in the negative ion mode; (d) TIC profiles of normal tissue in the negative ion mode. Red arrows indicate metabolites subsequently identified as having different abundances in the two groups. e Principal component analysis in positive ion mode. f Principal component analysis in the negative ion mode. Each dot represents a single sample. Red represents the tumor tissue, green represents the normal tissue, and blue represents the QC group. TIC, total ion current. QC, quality control group