AGR2 as a potential biomarker of human lung adenocarcinoma. 
The present study aimed to identify useful candidate biomarkers of lung adenocarcinoma for clinical diagnosis and treatment using proteomics technology.  We assessed frequently highly overexpressed proteins in 12 cases of lung adenocarcinoma compared with adjacent normal tissue samples by liquid chromatography tandem mass spectrometry (LC-MS/MS) coupled with isobaric tags for relative and absolute quantitation (iTRAQ) technology, and validated the expression of target proteins by immunohistochemistry in 268 lung adenocarcinoma cases.  Protein expression and clinicopathological variables were compared statistically for the evaluation of novel biomarkers.  One hundred seventy-seven proteins displaying significant quantitative changes compared with adjacent normal-appearing lung tissue were identified in more than 9 out of 12 lung adenocarcinoma patients.  Based on the results of liquid chromatography tandem mass spectrometry, Ingenuity Pathway, and immunohistochemical analyses, anterior gradient homolog 2 (AGR2) (upregulated 9.9-fold) was selected as a potential biomarker of human lung adenocarcinoma.  AGR2 was positive in 94% of lung adenocarcinoma patients.  Negative AGR2 expression was associated with poor survival (p = 0.007).  AGR2 is likely to become a biomarker for clinical applications.