Cancer pain, or cancer pain for short, is the pain caused by cancer, cancer-related diseases and anti-cancer treatment, and is one of the main sufferings of patients with advanced cancer. A considerable number of patients do not die directly from cancer, but from severe pain. There are many clinical causes of cancer pain About 65% of the pain is directly related to tumor, 25% of the pain is related to treatment, and other factors cause about 10% of the pain. For example: direct tumor compression and nerve stimulation; tumor bone metastasis; tumor stimulation of pain-sensitive tissues (blood vessels, lymphatic vessels, etc.); pain caused by tumor secretory factors, pain caused by accompanying inflammatory factors; pain after surgery, radiation therapy, chemotherapy and other treatments; psychosocial factors; pain caused by accompanying diseases, etc. The clinical manifestations of cancer pain vary according to the different locations, nature and stages of tumors. Persistent vague pain and swelling pain are the most common manifestations of late stage tumor pain, mostly seen in early stage visceral tumor pain; persistent vague pain accompanied by paroxysmal pain is the clinical manifestation of pain in cavity organs or tumors invading liver and bile ducts; persistent pain accompanied by spontaneous pain may be the clinical manifestation of pain in tumors invading peripheral nervous system; moderate or above persistent pain accompanied by paroxysmal pins-and-needles, band-like, knife-cutting or electric pain, If the patient has pressure pain in multiple parts of the sternum or ribs and wandering pain in multiple joints involving the elbow, wrist, knee and hip, he should be alert to leukemia and multiple myeloma. Patients who come to the clinic with pain as the main manifestation should have high suspicion of cancer pain in the following situations: the location of pain is relatively fixed, poor responsiveness to conventional drugs and treatments, pain is often obvious at night, progressive increase and sudden pain (eruption pain), especially in elderly patients and those with significant weight loss. Diagnosis of cancer pain Diagnosis of cancer pain is the basis of treatment of cancer pain. The procedure of diagnosis is the same as that of general diseases, including medical history, physical examination and laboratory tests. The main points of diagnosis include confirming the mechanism of cancer pain, characteristics of cancer pain, assessing the scope and degree of pain, distinguishing the nature of pain, and confirming the cancer pain syndrome. Only when these points are clearly diagnosed can a reasonable and effective treatment plan be formulated. The treatment of cancer pain emphasizes comprehensive treatment and individualized treatment, including etiological treatment, analgesic drug treatment, nerve block and destruction treatment, psychological treatment, etc. Drug therapy is the main means to relieve cancer pain, and the “WHO three-step pain relief principle” is the core of standardized cancer pain treatment. Three steps of pain relief refers to: the first step drugs for mild pain, i.e. non-opioid drugs, mainly non-steroidal anti-inflammatory and analgesic drugs, which have positive effect on bone and soft tissue pain treatment, no drug resistance and dependence, with capping effect and more side effects, so don’t increase the dose blindly; the second step drugs for moderate pain, i.e. weak opioid drugs, such as codeine and tramadol, which also have capping effect; the third step drugs for severe pain, i.e. strong opioid drugs, which have capping effect. Drugs, i.e. strong opioids, have no capping effect and should be titrated, commonly used are morphine controlled extended release, fentanyl transdermal patches, etc. The possibility of addiction is minimal with correct application, but dulcolax should not be used. Analgesic adjuvants can be added to all three ladders according to pain, including antidepressants such as amitriptyline and doxepin, anticonvulsants such as carbamazepine and gabapentin, NMDA receptor antagonist ketamine, α1 agonist colistin, antiarrhythmics such as lidocaine, mexiletine and glucocorticoids. For bone metastatic pain, the combination of NSAIDs, opioids and bisphosphonates has better effect.WHO stipulates that the five basic principles to be observed in cancer pain drug therapy are: preferred non-invasive route of administration (oral, transdermal patches, rectal suppositories), timely administration, stepwise administration, individualized administration, and attention to specific details. Standardized three-step drug therapy results in effective pain control in about 80% of cancer patients. The “WHO Three Step Pain Relief Principles” are the basic knowledge and skills that every medical personnel engaged in cancer pain management should master. Usually, cancer pain that cannot be controlled by three-step drug therapy, or cancer pain that cannot tolerate drug side effects and cannot continue drug analgesia is called refractory cancer pain, which must be treated with “three-step external therapy”, also known as “fourth-step therapy”, which is mainly minimally invasive treatment. It includes nerve block and destruction, spinal cord electrical stimulation, and central target-controlled analgesia. It includes peripheral nerve block and destruction, cervical, thoracic and lumbar sympathetic ganglion block and destruction, epidural nerve block and destruction, subarachnoid nerve destruction, abdominal plexus destruction and pituitary gland destruction. Destruction includes ethanol, phenol glycerin and other drug destruction and radiofrequency destruction. Radiofrequency destruction can also be used to directly destroy tumors and reduce pain. Spinal cord electrical stimulation and central target-controlled analgesia are considered the “ultimate therapy” for pain, but are expensive. Spinal cord electrical stimulation is effective for neuropathic and vascular pain, and central targeted analgesia is effective for a wide range of pain, especially for severe pain of a wide range. The “triple step extrapyramidal therapy” requires a specialized pain physician.