AFP and colorectal carcinoma: The CEA and α-fetoprotein (AFP) values were retrieved as auxiliary diagnosis for all the patients, and in the training set, the CEA of CRC patients was higher than the HV (P = 0.000, Mann–Whitney U test), while the AFP was lower in CRC patients (P < 0.01, Mann–Whitney U test), and in the validation set, the CEA (P = 0.000, Mann–Whitney U test) and AFP (P = 0.000, Mann–Whitney U test) were higher in the CRC patients compared with the HV.