I. Overview Pain is one of the most common symptoms of cancer patients, which seriously affects the quality of life of cancer patients. The incidence of pain in first diagnosed cancer patients is about 25%; the incidence of pain in advanced cancer patients is about 60%-80%, and 1/3 of them have severe pain. If cancer pain (hereinafter referred to as cancer pain) is not relieved, patients will feel extremely uncomfortable, which may cause or aggravate patients’ anxiety, depression, fatigue, insomnia, loss of appetite and other symptoms, and seriously affect patients’ daily activities, self-care ability, interaction ability and overall quality of life. In order to further standardize the treatment behavior of cancer pain in China, improve the standardized treatment system of major diseases, improve the level of cancer pain treatment in medical institutions, improve the quality of life of cancer patients, and guarantee medical quality and medical safety, this specification is formulated. II. Etiology, mechanism and classification of cancer pain (a) Etiology of cancer pain. The causes of cancer pain are diverse and can be broadly divided into the following three categories: 1. tumor-related pain: caused by direct invasion and compression of local tissues by tumor, and tumor metastasis involving bone and other tissues. 2. 2.Anti-tumor therapy-related pain: it is commonly caused by surgery, traumatic examination operation, radiation therapy, and cytotoxic chemotherapy drug treatment. 3. Non-tumor factor pain: including pain caused by other comorbidities, complications and other non-tumor factors. (B) Cancer pain mechanism and classification. 1. Pain is mainly divided into two types according to pathophysiological mechanism: injury-receptive pain and neuropathic pain. (1) Injury-receptive pain is pain caused by harmful stimuli acting on somatic or organ tissues and causing damage to the structure. Injury-receptive pain is associated with actual or potential tissue damage, and is the process of physiological nociceptive nerve information transmission and response that the body exhibits in response to injury. Injury-receptive pain includes somatic pain and visceral pain. Somatic pain often presents as dull, sharp, or pressure pain. Visceral pain usually manifests as diffuse pain and colic that is not sufficiently localized. (2) Neuropathic pain is caused by damage to peripheral or central nerves and abnormal nerve impulses in nociceptive transmission nerve fibers or pain centers. Neuropathic pain is often presented as stabbing pain, burning pain, discharge-like pain, shooting pain, numbness pain, paresthesia pain, shooting pain. phantom pain, central drop, and swelling pain, often combined with spontaneous pain, touch-evoked pain, nociceptive hypersensitivity, and nociceptive hypersensitivity. Chronic pain after treatment also belongs to neuropathic pain. 2. Pain is divided into acute pain and chronic pain according to the duration of onset. Most of the cancer pain is chronic pain. Compared with acute pain, chronic pain lasts longer, the etiology is not clear, the degree of pain and the degree of tissue damage can be separated, and it can be accompanied by nociceptive hypersensitivity, abnormal pain, and poor efficacy of conventional analgesic treatment. The mechanisms of chronic pain and acute pain have both commonalities and differences. In addition to the basic conduction modulation process of injury-receptive pain, chronic pain can also show neuropathic pain mechanisms different from acute pain, such as overexcitation of injury receptors, ectopic electrical activity of damaged nerves, over-sensitivity of central mechanisms of nociceptive transmission, abnormal expression of ion channels and receptors, and central nervous system remodeling. Cancer pain assessment is a prerequisite for reasonable and effective pain relief treatment. Cancer pain assessment should follow the principles of “routine, quantitative, comprehensive and dynamic” assessment. (A) Principle of routine assessment. Routine assessment of cancer pain means that medical and nursing staff should take the initiative to ask cancer patients whether they have pain, routinely assess their pain conditions and make corresponding medical records, which should be completed within 8 hours after admission. For cancer patients with pain symptoms, pain assessment should be included in the content of nursing routine monitoring and recording. Routine pain assessment should identify the causes of explosive episodes of pain, such as pain due to pathological fractures requiring special management, brain metastases, infections, and acute conditions such as intestinal obstruction. (b) Principle of quantitative assessment. Quantitative assessment of cancer pain refers to the use of quantitative criteria such as pain level assessment scale to assess the patient’s subjective pain level, which requires close cooperation from the patient. When quantitative assessment of pain, the focus should be on assessing the most severe and least severe pain level of patients in the last 24 hours, as well as the pain level of usual conditions. The quantitative assessment should be completed within 8 hours of the patient’s admission to the hospital. Quantitative assessment of cancer pain usually uses three methods: numerical rating scale (NRS), facial expression assessment scale, and pain rating of complaints (VRS). 1.Numerical Rating System (NRS): The Numerical Rating Scale of Pain Level is used to assess the pain level of patients. The degree of pain is expressed by 0-10 numbers in order, with 0 indicating no pain and 10 indicating the most severe pain. The patient chooses a number that best represents his or her pain level, or the healthcare provider asks the patient: How severe is your pain? The healthcare provider selects the corresponding number based on the patient’s description of the pain. The pain level is classified according to the number corresponding to the pain: mild pain, moderate pain, and severe pain. 2.Facial expression pain rating scale method: Pain assessment is performed by health care personnel according to the patient’s facial expression state when in pain and against the Facial Expression Pain Rating Scale, which is applicable to patients with expression difficulties, such as children, the elderly, and patients with language or cultural differences or other communication barriers. 3.Subjective pain grading method (VRS): according to the patient’s complaints of pain, the pain level is divided into three categories: mild, moderate and severe. (1) Mild pain: painful but tolerable, normal life, no disturbance in sleep. (2)Moderate pain: pain is obvious and unbearable, requiring analgesic drugs, and sleep is disturbed. (3)Severe pain: pain is severe and unbearable, analgesic drugs are required, sleep is severely disturbed, and may be accompanied by autonomic disorder or passive body position. (3) Principle of comprehensive assessment. Comprehensive assessment of cancer pain refers to the comprehensive assessment of pain condition and related conditions of cancer patients, including the cause and type of pain (somatic, visceral or neuropathic), pain episodes (nature of pain, aggravating or relieving factors), pain relief treatment, function of vital organs, psycho-spiritual condition, family and social support, and past history (e.g. history of psychiatric disease, history of drug abuse), etc. The first comprehensive assessment should be conducted within 24 hours after the patient is admitted to the hospital, and during the treatment process, another comprehensive assessment should be conducted within 3 days of giving pain relief treatment or when stable remission is achieved, in principle no less than 2 times/month. Comprehensive assessment of cancer pain usually uses the Brief Pain Assessment Inventory (BPI) (see Annex 1) to assess pain and its impact on patients’ mood, sleep, mobility, appetite, daily life, walking ability, interaction with others and other quality of life. Patients should be valued and encouraged to describe their needs and concerns about pain management, and to set goals for optimizing patient function and quality of life and individualizing pain management according to their condition and wishes. (iv) The principle of dynamic assessment. Dynamic assessment of cancer pain refers to continuous and dynamic assessment of changes in pain symptoms of cancer pain patients, including assessment of changes in pain level and nature, explosive pain episodes, pain reduction and aggravation factors, and adverse reactions to analgesic treatment. Dynamic assessment is especially important for dose titration of drug analgesic treatment. During the period of analgesic treatment, the type and dose of medication titration, pain level and changes in condition should be recorded. Cancer pain treatment (a) Treatment principles. The principle of comprehensive treatment should be adopted for cancer pain. According to the patient’s condition and physical status, pain relief treatment should be applied effectively to eliminate pain continuously and effectively, prevent and control the adverse drug reactions, and reduce the psychological burden caused by pain and treatment, so as to maximize the quality of life of patients. (II) Treatment methods. The treatment methods of cancer pain include: etiological treatment, pharmacological pain relief treatment and non-pharmacological treatment. 1. Etiological treatment. Treat the causes of cancer pain. The main causes of cancer pain are cancer itself, complications and so on. Anti-cancer treatment, such as surgery, radiotherapy or chemotherapy, is given to cancer patients, which may relieve cancer pain. 2.Drug pain relief treatment. Principle. According to the World Health Organization (WHO) guidelines for three-step pain relief treatment for cancer pain, the five basic principles of drug pain relief treatment for cancer pain are as follows: Oral administration. Oral administration is the most common route of drug delivery. For patients who are not suitable for oral administration, other routes of drug delivery can be used, such as subcutaneous injection of morphine, patient-controlled analgesia, and more convenient methods such as transdermal patches. Medication should be administered in steps. According to the patient’s pain level, analgesic drugs of different strengths should be selected in a targeted manner. ①Mild pain: non-steroidal anti-inflammatory drugs (NSAID) can be used. ②Moderate pain: weak opioids can be used, and NSAIDs can be used in combination. ③Severe pain: strong opioids can be used and NSAIDs can be used in combination. The use of opioids together with NSAIDs can enhance the pain relief effect of opioids and reduce the dosage of opioids. Strong opioids may also be considered for mild and moderate pain if good analgesia can be achieved without serious adverse effects. If the patient is diagnosed with neuropathic pain, tricyclic antidepressants or anticonvulsants should be preferred. 3. Timely administration of medication. Refers to the regular administration of pain medication at prescribed time intervals. Timely administration helps to maintain a stable and effective blood concentration. At present, the clinical use of controlled and slow-release drugs is becoming more and more widespread, emphasizing the use of controlled and slow-release opioid drugs as the basic medication for pain relief, and the immediate release opioid drugs can be given for symptomatic treatment when titration and outbreak pain occur. 4.Individualized drug administration. It refers to the individualized medication plan according to the patient’s condition and the dose of cancer pain relief drugs. When opioids are used, there is no ideal standard dose of opioids due to individual differences, and sufficient doses of drugs should be used according to the patient’s condition so that pain can be relieved. Also, the nature of neuropathic pain should be identified and the possibility of combined medication should be considered. 5. Pay attention to specific details. Patients using painkillers should be monitored closely to observe the degree of pain relief and the organism’s reaction, pay attention to the interaction of the combined application of drugs, and promptly take the necessary measures to minimize the adverse drug reactions with a view to improving the quality of life of patients. Drug selection and use method. According to the degree and nature of pain, the treatment being received and the concomitant diseases of cancer patients, we should reasonably select pain-relieving drugs and auxiliary drugs, individually adjust the dosage and frequency of drug administration, and prevent and control adverse reactions, so as to obtain the best pain-relieving effect and reduce the occurrence of adverse reactions. Non-steroidal anti-inflammatory drugs. Different NSAIDs have similar mechanism of action and have analgesic and anti-inflammatory effects, and are often used to relieve mild pain or combined with opioids to relieve moderate or severe pain. NSAIDs commonly used in cancer pain treatment include: ibuprofen, diclofenac, acetaminophen, indomethacin, celecoxib, etc. The common adverse reactions of NSAIDs include: peptic ulcer, gastrointestinal bleeding, platelet dysfunction, renal impairment, hepatic impairment, etc. The occurrence of their adverse reactions is related to the dose and duration of use. The daily limit doses of NSAIDs are: ibuprofen 2400mg/d, acetaminophen 2000mg/d, celecoxib 400mg/d. When using NSAIDs, the dose of medication reaches above a certain level, increasing the dose of medication does not enhance its pain-relieving effect, but the toxic reaction of medication will increase significantly. Therefore, if long-term use of NSAIDs is required, or if the daily dose has reached the restrictive dosage, replacement with opioid analgesics should be considered; if it is a combination, only the dose of opioid analgesics should be increased. Opioids. It is the drug of choice for moderate and severe pain treatment. At present, the short-acting opioids commonly used in cancer pain treatment are morphine immediate release tablets, and the long-acting opioids are morphine extended-release tablets, oxycodone extended-release tablets and fentanyl transdermal patches. For the treatment of chronic cancer pain, opioid agonists are recommended. For long-term use of opioid analgesics, oral route of administration is preferred, while transdermal absorption route can be used when there are clear indications, and temporary subcutaneous injection can be used. In the process of cancer pain treatment, the understanding and cooperation of patients and their families are crucial. Patients should be encouraged to describe the degree of pain to health care personnel; pain treatment is an important part of comprehensive cancer treatment, and pain tolerance is harmful to patients; most cancer pain can be effectively controlled by drug treatment, and patients should carry out pain treatment under the guidance of physicians; take drugs regularly, and it is not advisable to adjust the dose of painkillers and pain relief plan by oneself; morphine and its similar drugs are commonly used in cancer pain treatment. It is extremely rare that addiction is caused by the application of morphine drugs in cancer pain treatment; the safe placement of drugs should be ensured; the efficacy and adverse reactions of drugs should be closely observed during pain treatment, and medical staff should be communicated with at any time to adjust the treatment goals and treatment measures; regular follow-ups or visits should be made.