Cachexia is severe malnutrition. Loss of appetite and cachexia are often closely related and appear together. Loss of appetite is both a cause and a clinical manifestation of cachexia, so it is collectively called oncologic loss of appetite and cachexia syndrome (CACS). Loss of appetite is often the chief complaint of many oncology patients at their first visit. It is estimated that 25% to 40% of tumor patients have loss of appetite at the time of consultation, and up to 80% of advanced patients. Those with more weight loss have significantly higher postoperative complications and mortality, chemotherapy is less effective than those with the same stage of disease and histological type but without malnutrition, and chemotherapy produces more side effects than the latter. Patients with CACS have decreased immune function and are prone to infection. CACS often makes many anti-tumor treatments impossible and leads to total host organ failure, which becomes a direct cause of patient death. The main clinical manifestations of cachexia are anorexia, nausea, weight loss, anemia, muscle atrophy, and eventually the loss of all fat and muscle, leading to death. Anorexia is often an important component of cancer cachexia syndrome. Originally, anorexia was thought to be the main cause of wasting, but studies have found that anorexia is a result of cachexia rather than the cause. In conclusion, the clinical manifestations of cancer cachexia syndrome are firstly, loss of appetite or anorexia, and secondly, malnutrition. Some special signs of cachexia can also be seen, such as spatulate nail, anti nail, seen in iron deficiency; bruises, bruises, seen in vitamin C, vitamin K deficiency; hyperpigmentation, skin keratinization, seen in niacin and vitamin A deficiency; dry conjunctiva, seen in vitamin A deficiency; blepharitis, dry and cracked lips, corner of the mouth, seen in multiple B vitamin deficiency; lack of taste, taste disorder, seen in zinc deficiency; tongue inflammation This is seen in multivitamin deficiency; bleeding gums, seen in vitamin C deficiency; enlarged parotid glands, seen in protein deficiency; enlarged thyroid gland, seen in iodine deficiency; tachycardia, enlarged heart, heart failure, etc., may be due to severe anemia or vitamin B1 deficiency; muscle pain, seen in protein deficiency and vitamin B1 deficiency; abnormal sensation, nutritional polyneuritis, may have vitamin B1, B6, B12, and niacin deficiency; wounds, seen in vitamin A deficiency; wound, seen in vitamin C deficiency; gingival bleeding, seen in vitamin C deficiency. B12 and niacin deficiencies; wounds that do not heal for a long time or slow tissue repair are due to vitamin C, zinc, protein and caloric deficiencies.