Diagnostic algorithm

To construct the diagnostic algorithm of GC, logistic regression (LR), a type of machine learning method, was used for discriminant analysis. The expression levels (peak area in the chromatogram) of 536 lipid molecules obtained from each plasma sample were individually normalized by the median value. The normalized datasets of control and cancer were learned by LR, and blinded samples were classified as cancer or not. The cancer possibility was indicated as the probability value (0.0–1.0). The procedure and mathematical formulae used were those described in our previous study (27). The predictive accuracy of the LR classifier was evaluated by using a leave-one-out cross validation (LOOCV) procedure (28). These procedures are shown in Fig. S2.