DDX55 and cancer: Among urinary proteins with aberrant expression in the comprehensive proteomics analysis, we finally selected seven urinary protein candidates (TFF1, PGA3, BARD1, CCDC38, TINAGL1, NDRG1 and DDX55) for next-step analysis, which fulfilled the following criteria from previous reports and databases including The Cancer Genome Atlas, The Human Protein Atlas and GeneCards: protein with small molecular weight; and cancer/testis antigen or proteins specifically expressed in stomach (Fig. 1d).