Lung cancer is one of the most prevalent and fatal types of cancer, with average 5-year survival rates lower than 15%, 1,2 which is mainly due to the advanced stage at which lung tumors are usually diagnosed. Indeed, when lung cancer is detected before metastasizing to lymph nodes or distant sites, the 5-year survival rates increase drastically to 60À80%, thus stressing the importance of early diagnosis. However, the majority of patients show no signs or symptoms during the initial phases of neoplastic growth, hindering early detection and the possibility of curative surgical treatment. Moreover, radiological tests, such as computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET), which would allow the detection of initial cancer lesions, are not suitable for general screening of the population, mainly due to their high costs. Therefore, new methods that can aid in the early detection of lung cancer and contribute to improved prognosis are greatly needed.The search for metabolic markers of cancer in human tissues and biofluids has been the focus of a number of metabonomic studies in recent years. 3,4 In particular, metabolic profiling of blood plasma or serum has been increasingly used to unveil metabolic alterations associated with different cancer types, such as breast, 5À7 kidney, 8À10 liver, 11À13 prostate, 14À16 colorectal, 17À20 oral, 21,22 pancreatic, 23,24 esophageal, 25 and bone 26 cancers. In the case of lung cancer, only a few studies focusing on plasma or serum metabolic profiling have been recently reported. Maeda and co-workers proposed that the differences in the plasma amino acid profiles between healthy controls and non-small-cell lung cancer (NSCLC) patients, as assessed by targeted liquid chromatography coupled to mass spectrometry (LCÀMS), could potentially be useful for screening NSCLC. 27 In another MS study of specific compounds, namely, lysophosphatidylcholines (lysoPC), abnormal levels of lysoPC isomers with different fatty acyl positions were found in the plasma of lung cancer patients compared to controls. 28 Using a more global profiling approach, Jordan and colleagues reported the NMR analysis of paired tissue and serum samples from 14 subjects with two different lung cancer histological types (adenocarcinoma and squamous cell