There are many causes of weakness and nausea, but they are not specific enough to diagnose early cancer based solely on weakness and nausea. Weakness and nausea can occur in many common diseases. Common causes of weakness and nausea include heat stroke, acute gastroenteritis, high blood pressure, hypoglycemia, hepatitis and so on. Most cancers have no obvious symptoms in the early stages and are not easy to be detected early. Most patients will gradually experience unexplained weight loss, anorexia, body weakness, and some patients will experience irregular fever. As the disease develops, different parts of cancer will have different symptoms, such as lung cancer may have cough, blood in sputum or hemoptysis, chest pain, chest tightness, etc.; gastric cancer may have nausea, vomiting, abdominal pain, loss of appetite, and fatigue, etc.; and colorectal cancer may have bloody stools, abdominal pain, diarrhea and other symptoms. Colorectal cancer can have symptoms such as bloody stool, abdominal pain and diarrhea. With the development of medical science and advancement of detection means, early detection, early diagnosis and early treatment can effectively improve the survival period and quality of life of cancer patients. It is recommended to have regular health checkups, and if cancer is suspected in health checkups, relevant tests can be carried out in time to make it clear.