The occurrence of liver metastasis after curative surgery for resectable colorectal cancer is an important cause of death for patients. Accurately identifying high-risk patients for metastasis and intervening in them has important clinical significance. The pathological examination of surgical specimens failed to fully utilize valuable specimen information and accurately predict liver metastasis; The biomarkers secreted by tumors are metabolized in the liver through the portal vein, especially the particles such as extracellular vesicles secreted by tumors, which are ultimately diluted in peripheral blood and cannot be effectively detected. Our research group extracted an average of 11.25ml of blood (named blood derived from portal vein branch specimens, sdBlood for short) from 8 colorectal cancer radical surgery specimens. Compared with peripheral blood, protein mass spectrometry analysis revealed a significant increase in exosome proteins such as peroxidized redox protein 1 (PRDX1), which are highly correlated with metastasis. This project innovatively uses sdBlood, which has been overlooked by routine pathological examination, to detect the exosomal protein PRDX1 in sdBlood, which is significantly higher than the peripheral blood concentration. A prospective cohort study was established, including 252 patients with pathologically confirmed colorectal cancer after radical surgery. The incidence and time of liver metastasis were followed up and observed. Cox regression statistical analysis was used to determine the correlation between this marker and metastasis and determine its critical value, providing a basis for clinical diagnosis and treatment.