PDAC and CP blood samples have been compared by LC-MS metabolomics analysis in two previous studies (Urayama et al. 2010; Fukutake et al. 2015). One of these targeted free amino acids in plasma. The advantage of a targeted approach is that sample preparation and analysis is optimized for a specific class of metabolites, but at the cost of covering only a limited part of the metabolome. Untargeted LC-MS on the other hand has the largest potential to identify novel metabolites due to increased metabolome coverage (Patti et al. 2012). In the second previous study comparing PDAC and CP, untargeted LC-MS was applied to plasma samples. Contrary to the present study, clinical data on e.g. disease stage and smoking status was available, which is important to avoid known confounding factors; however, the sample size (n = 10) was very limited which makes the results less generalizable. Other studies have applied different analytical metabolomics platforms to discriminate PDAC and CP in bodily fluids. In a study using gas chromatography-mass spectrometry, a majority of the serum discriminative metabolites were amino acids (Kobayashi et al. 2013), but included also some metabolites that would not have been particularly well captured in our LC-MS set-up such as some sugar species including, arabinose, ribulose and 1,5-Anhydro-D-glucitol and some organic acids such as uric acid, nonanoic acid and caprylic acid. In the mentioned study, CP samples were however included in the validation cohort only. Amino acids were also connected to future risk of pancreatic cancer in a metabolomics study applying LC-MS to prediagnostic plasma (Mayers et al. 2014). In the present study a number of amino acids were found dysregulated in PDAC compared to CP in the validation cohort only (data not shown), but lacking confirmation in a second cohort these results were excluded. Further, two studies have used nuclear magnetic resonance to study plasma and urine samples, respectively, but have not validated their results in a second cohort (Zhang et al. 2012) or had only three CP samples out of a total of 25 samples included in the benign control group (Davis et al. 2013).