AFP and hepatocellular carcinoma: In the Shanghai cohort, 47 of 137 HCC patients (35.77%) were AFP negative (AFP < 20 ng/ml, stage I n = 18, stage II n = 17 and stage III n = 12); 11 of 94 PAAD patients (11.70%) were CA19-9 negative (CA19-9 < 37 U/ml, stage I n = 2, stage II n = 7, stage III n = 1 and stage IV n = 1); 109 of 232 CRC patients (46.98%) were CEA negative (CEA < 5 ng/ml, stage I n = 24, stage II n = 35, stage III n = 22 and stage IV n = 28) and 149 of 230 CRC patients (64.78%) were CA19-9 negative (CA19-9 < 37 U/ml, stage I n = 24, stage II n = 47, stage III n = 25 and stage IV n = 53).