The role of the three routine laboratory tests of blood, urine and stool to screen for cancer should not be taken lightly. For patients with anemia, anemia may be a manifestation of gastric cancer or colon cancer; excessive white blood cells and childish white blood cells found in peripheral blood picture should be considered as leukemia, and the type of leukemia can be classified according to its type, or it may be a leukemia-like reaction. If R-S cells are found in the peripheral blood picture it is a diagnostic clue for Hodgkin’s disease; if heterogeneous histiocytes are found it suggests the possibility of malignant histiocytosis. Tumors of the urinary system often have red blood cells seen in routine urine. In patients with myeloma, urinalysis may be positive for Benzo’s protein. Early signs of cancer in the digestive tract may manifest as varying degrees of occult blood. The presence of mucus and red blood cells in the stool should be considered as a possible rectal cancer. A long-term positive stool routine + occult blood test indicates the possibility of gastrointestinal cancer.