Gastrointestinal tumors, including esophageal cancer, gastric cancer, and colorectal cancer, are among the most common and highly prevalent malignant tumors in Shandong Province. Currently, most patients seek medical attention only after clinical symptoms appear, by which time the disease has already reached an intermediate or advanced stage. This leads to increased treatment costs and poorer therapeutic outcomes. Early detection and intervention through screening are effective measures to improve the cure rate of gastrointestinal tumors and reduce their incidence and mortality rates. This project leverages the Shandong Province Tumor Screening and Early Diagnosis \& Treatment Platform and is based on the ongoing Shandong Gastrointestinal Cancer Screening Cohort. It aims to collect 4,000 plasma samples from individuals undergoing simultaneous screening for esophageal, gastric, and colorectal cancers. Using Nanjing Shihe Medical Laboratory's independently developed multi-cancer early detection liquid biopsy product for gastrointestinal cancers, the study will further validate the performance of liquid biopsy in multi-cancer screening by correlating results with endoscopic findings (gastroscopy and colonoscopy).