It is common for cancer patients to experience this kind of pain, and almost most of them will experience pain in the advanced stages. The main reason for the pain is the progression of the tumor, which constantly invades the surrounding tissues and this causes pain. Tumors that invade the surrounding nerve tissue, organs, and bone tissue can cause very severe pain. So about 90% of patients will have pain in the late stage. There are three main mechanisms of pain caused by cancer 1. Pain caused by cancer development: the tumor invades the nerves, tubular organs, vascular system, bone marrow and so on, as well as the tumor itself secretes pain-causing substances. 2. Pain after cancer treatment: pain can be caused after surgery, radiation therapy and chemotherapy; and psychological factors. Pain is an unpleasant feeling in human, and the existence of psychological factors has been neglected before, while patients may aggravate the subjective feeling of pain due to depression, anxiety, and so on. 3. Combination of chronic painful diseases: it refers to the combination of arthritis, cervical spondylosis, lumbar intervertebral disc herniation, etc. on the basis of cancer, which is not necessarily cancer-induced pain, but may be caused by these slow, or superimposed on each other and become more painful. Occurrence of cancer pain site: 45% in soft tissue (muscle, etc.), 35% in bone, 33% in viscera; 34% in neuropathic; 6% in unknown cause. 1/3 or more patients have pain in more than 2 1-2 sites. Cancer pain-causing factors: include many factors, among which direct tumor invasion, stimulation of tumor tissue products, metastases (bone, liver, lung metastases), nerves (injury, edema, compression, etc.) and treatments (surgery, intervention, puncture, radiotherapy, etc.) accounted for about 90%; unknown causes accounted for 8-10%. Sensory injurious stimulation: when the tissue cells are damaged by various reasons, it will stimulate the environment in the body to produce more prostaglandins, and the increased synthesis of prostaglandins will stimulate the sensory nerve endings to produce sensory injurious stimulation, and this stimulation is transmitted upward along the sensory nerves to produce the sensation of pain.