Fig. 2.

Metabolic biomarkers for detection of early lung tumor and evaluation of different histological types. (A) 46 influential metabolomic biomarkers with statistical significance of Stage I lung tumor patients (mean value with SD). Through Mann–Whitney U test, 46 influential metabolic biomarkers showed statistically significant difference (p-value<0.05) among 61 metabolites. (B) PCA of 10 metabolomic biomarkers in early lung tumor detection. It revealed a clear separation between stage I lung tumor patients and healthy individuals. (C) ROC curve of metabolomic biomarkers and combined variates in early lung tumor detection. The combination of six variates included proline, l-kynurenine, spermidine, amino-hippuric acid, palmitoyl-l-carnitine and taurine. (D) ROC analysis of metabolomic biomarkers and combined variates of adenocarcinoma (n = 63) and squamous carcinoma (n = 41) patients. The combination of four variates included hypoxanthine, l-Kynurenine, proline and Carnitine. SD, standard deviation. PCA, principal component analysis. ROC, receiver operating characteristic.