In the present study, the levels of a number of phospholipids were altered in PDAC compared to CP in both cohorts. Phospholipids were also found dysregulated in previous studies (Urayama et al. 2010; Ritchie et al. 2013; Sakai et al. 2016). However, we excluded all phospholipids as potential markers since they were down-regulated in PDAC in the discovery cohort as opposed to up-regulated in the validation cohort (Figs. 2, 4c, d). A possible explanation for these results is that different blood sample matrices, i.e. serum and plasma, were used in the two cohorts. Serum and plasma samples from the same individual are known to display different concentration levels for some metabolites, including phospholipids, due to the differences in sample handling (Yu et al. 2011). Noteworthy, as systemic phospholipid levels are altered by inflammatory responses in general, they are unlikely candidates for disease specific markers (Lindahl et al. 2016).