Fig. 1

The difference in preoperative levels of PPIA and B2M, stratified for patient group and UICC. cfDNA levels depicted as boxplot showing median, upper and lower quartiles. Whiskers extend into a max of 1.5 times the interquartile range. Observations outside this are displayed as outliers. Wilcoxon rank-sum test was used for analyzing the difference between groups, Kruskal–Wallis test for difference across groups. A shows the difference in B2M levels across and in-between patient groups. B shows the difference in PPIA levels across and in-between patient groups. C and D depict the difference in B2M and PPIA levels stratified for the UICC stage. PPIA: Peptidyl-Prolyl cis–trans Isomerase A, B2M: Beta-2-microglobulin, cfDNA: cell-free DNA, UICC: Union for International Cancer Control