Fold-change comparison between cohorts. Following confirmation of metabolite significance in the validation cohort (Fig. 1, step 4a and b), fold-change calculations revealed that eight metabolites were regulated in opposite directions in the discovery- and validation cohorts. All eight metabolites were phospholipids that were down-regulated in PDAC compared to CP in the discovery cohort, but up-regulated in PDAC compared to CP in the validation cohort. Consequently all phospholipids were excluded as potential single metabolite markers