Cancer generally has no pre-signs, and there are basically no obvious symptoms in the early stage. However, if there is obvious weight loss within a short period of time, abnormal fatigue, unexplained pain, etc., you can consult a doctor in time. 1. Obvious weight loss in a short time: If there is a significant weight loss in a short time without dieting, it may suggest the existence of cancer cells; repeated anorexia, vomiting, diarrhea and other symptoms are common in stomach cancer, colorectal cancer, and so on. 2. Abnormal fatigue: if the body feels fatigue despite sufficient rest and balanced nutrition, attention should be paid to the fatigue caused by chronic blood loss due to cancer. 3. Unexplained pain: pain in a certain part of the body that lasts for a long time and is not easy to be relieved, accompanied by low-grade fever, etc., should be alerted to the possibility of cancer. It is recommended to participate in early cancer screening regularly for early detection, diagnosis and treatment. Meanwhile, if you feel unwell, you should consult a doctor in time to improve the examination, make a clear diagnosis, and take active treatment in order to avoid delaying your condition.