Cancer is a new organism that is separated from the normal control of human body and grows indefinitely. Cancer has its inherent biological characteristics that are different from benign tumors, which are mainly manifested clinically in infiltration and metastasis, and the higher the degree of malignancy, the faster its growth and the stronger its ability to infiltrate and metastasize. As a result of infinite development and growth of cancer, on one hand, the body is continuously deprived of nutrients, which causes the body to be consumed infinitely and gradually weakened; on the other hand, the infiltration and metastasis of cancer cause corresponding damage to the functions of the organs involved, and eventually the organs fail to function and the body dies. It can be said that, unlike cardiovascular and cerebrovascular diseases, the harm of cancer to human body is mostly indirect, and most patients with cancer eventually die because of the functional failure of the affected organs. There is still a long period of time from the appearance of cancer to the failure of the involved organs and the death of the body. Therefore, when the involvement of the digestive tract is more prominent and functional insufficiency occurs, which directly endangers life, timely and reasonable nutritional support is of certain clinical significance. This is the starting point of nutritional support for Holocaust patients. Just because the harm of cancer to human body is indirect, the human body’s response to cancer is also very slow and easy to be ignored. Cancerous tissues evolve from the body’s own tissues, which basically do not produce stronger irritants and the body is compatible with them. Therefore, when the tissue cells of one of the organs of a person are just cancerous, the person will not feel any discomfort. When the cancer develops enough to affect the function of the involved organs, various discomforts, i.e. clinical symptoms, will appear depending on the involved organs. Even so, it is not easy to attract attention because some discomfort is easily tolerated or can be relieved by simple symptomatic treatment. At the same time, the dull sense of localization and pain of internal organs increases the invisibility of the occurrence and development of cancer tissue. The clinical symptoms will be more obvious only when the dysfunction of the affected organs becomes difficult to maintain normal life activities. Therefore, clinically, there are many cases of progressive or advanced stage cancer, but relatively few cases of early stage cancer. There are two main reasons for malnutrition, one is the direct impact of cancer on the body, which mainly includes the seizure and consumption of nutrients by cancer, metabolic abnormalities caused by toxins released by cancer, bleeding and infection caused by tissue destruction caused by cancer, etc., and the other reason is the indirect impact of cancer on the body. The other reason is the indirect effect of cancer on the body, its infiltration and metastasis involving the digestive tract, which affects the digestive and absorption functions of the digestive tract. The malnutrition of patients with malignant tumors unrelated to the digestive tract is basically caused by the direct influence of the cancer on the body, such as osteosarcoma, lung cancer, etc., which usually appears only when the cancer is more advanced; while the malnutrition of patients with malignant tumors related to the digestive tract is related to both the direct influence of the cancer on the body and the degree of functional involvement of the digestive tract. The closer the relationship between cancer and digestive and absorption functions, the earlier the impact on digestive and absorption functions appears, and the more likely to cause malnutrition. For example, malnutrition of gastric cancer growing near the pylorus may occur when the tumor is small because its growth into the cavity affects gastric emptying and causes pyloric obstruction, and the malnutrition of such patients is almost entirely caused by the involvement of the digestive tract and has little relationship with the direct impact of the cancer on the body. Therefore, it is more closely related to the digestive and absorption functions. Therefore, gastric cancer and esophageal cancer in the upper gastrointestinal tract, which are closely related to digestion and absorption, are most likely to cause malnutrition, while colorectal cancer is relatively rare. Other systemic cancers that can directly infiltrate or metastasize to the digestive tract are already at a rather advanced stage, and the proportion of malnutrition caused by their direct effects on the organism is greater than that of the cancer on the digestive tract. It is important to identify the causes of malnutrition for the implementation of clinical nutrition support. The existence of cancer is the root cause of malnutrition. Without complete removal of cancer or effective treatment of cancer, the direct effect of cancer on the body cannot be fundamentally interrupted, and clinical nutritional support can only improve the nutritional status to some extent, but it is impossible to completely correct it. At the same time, most of these patients are advanced or recurrent cases, lacking effective treatment means, and the cancer may affect all systems to a certain extent. In the case of malnutrition with GI tract involvement, nutrition support with reasonable formula can replace the function of GI tract, which can better improve the nutritional status of the patient, or lay the foundation for subsequent treatment, or achieve the purpose of prolonging the survival time and improving the quality of life. For example, for the above-mentioned gastric cancer with pyloric obstruction located in the pylorus, we usually establish the nutritional support route by endoscopically guiding the transnasal intestinal nutrition tube over the stenosis caused by the cancer, and perform enteral nutritional support by nasal feeding, because the general condition of the patient is not greatly affected by the cancer and the nutritional status can be easily improved. Clinically, nutritional support can be divided into three major categories according to the causes of malnutrition, the degree of digestive tract involvement, the location, nature and degree of tumor. The first category is adjuvant therapeutic nutritional support. Cancer can be treated, but before or during the treatment, patients with Holocaust are accompanied by more serious malnutrition, which makes effective treatment impossible to be implemented, and it is also impossible to limit the continued development of tumor, and the continued development of tumor aggravates malnutrition, which presents a vicious circle between the two. For example, in resectable cardia and sinus cancer cases with obstruction as the main symptom, the impact of cancer on the digestive tract is more prominent, and malnutrition is more obvious in some cases at the time of consultation, which makes surgery and other operations impossible. At this time, nutritional support becomes a breakthrough to interrupt this vicious circle and create favorable conditions for effective treatment of cancer. In complete obstruction, even parenteral nutrition support is worthwhile, as long as the cancer can be treated effectively afterwards. In the case of head and neck cancer, if laryngeal edema and difficulty in eating occur during the course of radiotherapy, which makes it difficult to continue treatment, endoscopic percutaneous gastrostomy (PEG) for enteral nutrition can ensure the continuation of radiotherapy [1]. Effective treatment for the tumor is the key to treatment, and nutritional support is necessary, so it is called adjuvant therapeutic nutritional support. It is also the most recommended form of nutritional support for Dutch cancer patients. The key to whether nutritional support can become an adjuvant therapy in clinical practice is whether it can effectively treat the cancer afterwards, and the fundamental point of the controversy of nutritional support for Dutch cancer patients is that nutritional support may stimulate tumor growth while there is a lack of effective methods to curb tumor development in clinical practice. In fact, adjuvant therapeutic nutritional support is the key to effective treatment of cancer. In fact, adjuvant therapeutic nutritional support is not limited to resectable cancers such as gastric cancer and esophageal cancer, which are closely related to digestive and absorption functions, as mentioned above, but can play an adjuvant therapeutic role even for advanced cancers, as long as effective therapeutic means are available. In the past two years, we have achieved very satisfactory clinical results in neoadjuvant chemotherapy for unresectable advanced gastric cancer with mainly lymph node metastases by combining arteriovenous FLEP method [2], and for those cases with malnutrition that cannot be directly treated with neoadjuvant chemotherapy and those cases with malnutrition during the course of chemotherapy, nutritional support has been provided according to specific conditions, so that effective FLEP neoadjuvant The tumor and its metastases were reduced in size so that their direct effects on the body were lessened, while the symptoms of obstruction in the digestive tract were also relieved. In this way, while the tumor shrinks and can be resected, the patient’s general condition is improved, allowing the surgery to be performed safely. The second category is palliative nutritional support, where the cancer is advanced or relatively more limited recurrent cancer, there is no effective treatment, the development of cancer is mainly in the digestive tract, and malnutrition caused by serious involvement of digestive and absorption functions is more prominent and directly threatens life, while the functions of other organs are still available. Nutritional support for such patients to replace the function of the part of digestive tract involved by cancer can prolong patients’ life and improve their quality of life, although there is no effective treatment for the tumor. For example, endoscopic percutaneous gastrostomy (PEG) for enteral nutrition support in patients with unresectable esophageal or cardia cancer; dilation or stenting of cancerous strictures to restore enteral nutrition or diet in patients with unresectable esophageal cancer; jejunostomy for enteral nutrition in patients with local recurrence of cancer resulting in obstruction of the remnant stomach or jejunal strictures, etc. Nutritional support itself does not have any therapeutic effect on the tumor, but it can replace the digestive and absorption functions affected by cancer to a certain extent, so that before the functions of other organs are affected by cancer to a serious life-threatening level, the lotus cancer organism will not die due to malnutrition, so it is called palliative therapeutic nutritional support. The fundamental difference between palliative therapeutic nutritional support and adjuvant therapeutic nutritional support lies in the availability of effective treatment methods for tumors. After the nutritional support reaches its goal, if it can effectively treat and control the tumor, it is adjuvant therapeutic nutritional support; otherwise, it is palliative therapeutic nutritional support. Palliative therapeutic nutritional support is also worth advocating in clinical practice, because it can achieve the purpose of prolonging patients’ life and improving their quality of life. The fewer and lighter the organs involved in cancer, the greater the significance of palliative therapeutic nutritional support, because at this time, the survival time and quality of Holocaust patients depend on the number and degree of other organs involved in cancer. The third category is anwai therapeutic nutritional support, which is not only related to the direct impact of cancer on the body but also related to the extensive involvement of the digestive tract, so nutritional support instead of partial digestion and absorption can neither improve the nutritional status ideally nor relieve the threat to the body caused by the impaired function of other organs. Nutritional support instead of digestion and absorption can neither improve the nutritional status nor relieve the threat of impaired function of other organs. For example, local recurrence of gastric cancer causes multiple obstruction in the small intestine, colon and common bile duct that are adhered to the original surgical field; peritoneal seeding recurrence of gastric or intestinal cancer causes multiple and segmental obstruction in the small intestine, and so on. Firstly, it has no therapeutic significance for the tumor; secondly, besides the gastrointestinal tract, malnutrition also comes from the direct impact of cancer on the body, and besides malnutrition, the threat to life also comes from the damage of cancer on other organ functions. Therefore, it is difficult for nutritional support to fundamentally improve the patient’s general condition; third, in cases where the digestive and absorption functions are relatively prominently affected, after their functions are partially replaced, the nutritional status may be improved to some extent, but it is difficult to achieve the purpose of prolonging life and improving the quality of life; fourth, it involves social and ethical aspects, as patients with advanced lotus cancer need to endure various pains during their survival Fourth, it involves social and ethical issues, as patients with advanced cancer need to endure various kinds of pain and suffering during their survival, and also includes the waste of social and economic resources, etc. Therefore, it is not worthwhile to advocate the use of antiretroviral nutritional support, which should be considered according to the patient’s specific situation and the wishes of the patient’s family. In clinical practice, adjuvant therapeutic nutritional support is the most recommended one, followed by palliative nutritional support, while anamnesis nutritional support needs to be carefully considered according to the specific situation. As human research and understanding of tumor continue to deepen, new and effective treatment methods will be introduced continuously, just like the case of gastric cancer with severe lymph node metastasis that was abandoned for treatment in the past, which can be changed from unresectable to resectable after chemotherapy with FLEP method, the number of effective treatment methods for advanced tumor will also increase, and then more and more cases of adjuvant therapeutic nutritional support will be provided clinically. The number of clinical cases of adjuvant therapeutic nutritional support will be increasing. The timely and reasonable nutritional support for tumor patients will create more favorable conditions for the effective treatment of tumor and make the treatment safer and more ideal.