Cancer screening through blood is mainly performed to diagnose some cancers with tumor markers. For example, AFP can help to diagnose primary liver cancer, CA125 can help to diagnose ovarian cancer, CA199 can help to diagnose pancreatic cancer, colorectal cancer, and CEA can help to diagnose gastric cancer, colorectal cancer, or some lung adenocarcinoma. However, it is worth noting that except for AFP which is specific for the diagnosis of liver cancer, all other tumor markers can only play a role in suggesting the diagnosis. Alpha-fetoprotein plus occupying lesions on ultrasound, CT or MRI can help diagnose primary liver cancer. However, elevated CA125 only suggests the possibility of ovarian cancer, whether it is or not still needs to be confirmed by pathology, as do CA199 and CEA.