The presence of cancer cells in the blood indicates that two conditions are occurring in the patient. In the first condition, suffering from leukemia, including acute leukemia and chronic leukemia, immature cancer cells can be found in the blood through blood smear examination. Especially in acute leukemia, a large number of immature cancer cells can be found in the blood smear, so once cancer cells are found in the blood, there are often manifestations of blood cancer. In the second case, cancer cells can also be found in the blood when blood metastasis occurs in malignant tumors in other parts, such as stomach cancer, liver cancer, lung cancer, prostate cancer and so on. These malignant diseases will have blood metastasis in the late stage and metastasize to distant organs through blood, and cancer cells can also be found in the blood. If cancer cells are found in these tumors, it often indicates that the malignant tumor has reached the late stage.