The disease with the worst prognosis is not leukemia. Clinically, the 5-year survival rate is commonly used to assess the prognosis of a disease, i.e. the survival rate of patients suffering from a certain disease after 5 years. 1. Leukemia is a malignant tumor of the blood system, including acute leukemia and chronic leukemia, and the prognosis of acute leukemia is worse than that of chronic leukemia. Current data show that acute leukemia is not the tumor with the worst prognosis. The 5-year survival rate of acute myeloid leukemia is 30.5%, while acute lymphoblastic leukemia can reach 70.8%. 2. Tumors with a 5-year survival rate of less than 30% include pancreatic cancer (11.5%), hepatocellular carcinoma and intrahepatic cholangiocarcinoma (20.8%), esophageal cancer (20.6%) and lung cancer (22.9%). When clearly diagnosed with malignant tumors, one should build up personal confidence, actively listen to the doctor’s advice, and actively treat under the doctor’s guidance, in order to get better treatment results.