In most cases, as long as cancer will cause long-term low fever of varying degrees, typically manifested as afternoon fever, i.e. no fever in the morning, but fever in the afternoon and evening, usually not higher than 38.5℃. The common ones are cancers of respiratory system, digestive system, lymphatic system, hematological system and reproductive system: 1. Cancer of respiratory system: such as lung cancer. Patients with lung cancer who have concurrent obstructive pneumonia or cancer metastasis and compression, causing local inflammation around them, will have clinical manifestations of long-term fever, which generally manifests as low body temperature, relatively fixed fever time, and also accompanied by cough, coughing and difficulty in breathing; 2. Cancer of digestive system Cancers of colon cancer and gastric cancer can cause long-term low fever of different degrees, which is generally caused by inflammation caused by necrosis on the surface of tumor, and also accompanied by gastrointestinal discomfort, such as epigastric pain, fullness, indigestion, etc.; 3. Cancers of lymphatic system: long-term low fever caused by lymphatic tumor is mainly due to the stimulation of thermoregulatory center by metabolic necrotic part of lymphatic tumor, which leads to long-term low fever, and may also be caused by Lymphoma patients have low immunity after long time chemotherapy, leading to long-term low fever triggered by infection from external factors, which may be accompanied by night sweats, fatigue, weight loss and other manifestations; 4. Cancer of hematological system: it will make most blood cells lose their functions, among which neutrophils in white blood cells lose their phagocytic effect on external infectious substances, leading to long-term low fever caused by external infections in patients, such as leukemia, which may appear pale face and anemia; 5. Cancer of reproductive system: such as ovarian cancer and cervical cancer in women, prostate cancer in men, etc., which may cause long-term low-grade fever due to tumor bleeding or necrotic infection, and need to improve pathological examination for clarification. In addition, cancers such as liver cancer and nasopharyngeal carcinoma may show long-term low fever, and patients need to go to hospital for examination and treatment in time to achieve better treatment effect. However, note that long-term low fever is not necessarily caused by cancer, but may also be caused by bacterial or viral infections such as colds, pneumonia, or urinary tract infections or pelvic infections, as well as autoimmune system diseases such as rheumatoid arthritis and lupus erythematosus, all of which may present with long-term low fever. Therefore, long-term low fever cannot be used as a basis for determining cancer. Patients need to seek timely medical attention to improve relevant examinations and clarify the cause of the disease so as to carry out targeted treatment.