CLDN4 and neoplasm: In fact, there is lack of knowledge on how to apply tumor markers, and the problem of defining an identikit of a tumor cell is also present in pathological anatomy where many PDAC markers are available: PTX3, LGALS9, ENO1, REG4, POSTN, CA242, LGALS1, SERPINB5, pVHL, CA125, MUC5AC, THBS2, LTBP2, CPA4, IMP3, CD13, DKK1, KOC, S100P, MSLN, MUC1, MUC4, PAM4, CA19-9, GPC-1, ANXA10, CLDN18, KRT19, KRT7, KRT17, CEA, and CLDN4 [72,73,74].