People with cancer pain usually experience more than one type of pain. This pain may be constant or intermittent, or acute pain superimposed on chronic pain. The pain may be disease-related or treatment-related. Psychological factors, such as depression and anxiety, as well as cognitive forms, may influence pain perception and increase pain intensity. Multiple factors contribute to pain in cancer patients: 1. Tumor expansion causes pressure on surrounding tissues. 2, Tumor secretion of inflammatory and pain sensitizing factors. 3, Tumor infiltration in the nerve plexus and damage to nerve tissue may cause neuropathic pain. 4.Bone metastatic spread of cancer is one of the most common causes of cancer pain. 5.Stretching of hollow viscera, distortion of solid organ sacs, inflammation of mucous membranes as well as local ischemia or necrosis activate visceral injurious receptors, leading to visceral pain. 6, Rapid weight loss, excessive muscle catabolism, immobilization, or increased muscle tone cause muscle pain. Bone metastases can cause painful muscle spasms. 7, Explosive pain, defined as an instantaneous pain episode that occurs over and above relatively well-controlled baseline pain , is very common. This can be due to a number of reasons, for example, bone metastases that cause pain with movement. Treatment-related pain. 8, Adverse effects of treatment include joint pain following chemotherapy and hormone therapy, and painful mucositis due to radiation therapy and chemotherapy with certain drugs. Possible forms of neuropathic pain occur: plexopathy after radiotherapy, peripheral polyneuropathy after chemotherapy, or chemotherapy drug-induced nociceptive hypersensitivity. 9, Surgical interventions may cause nerve damage and chronic postoperative pain. The pathophysiology of cancer pain is very complex and includes: 1. Local and systemic inflammatory responses that lead to the production of inflammatory cytokines that promote pain transmission. 2. pain directly related to the tumor : Cancer cells can cause invasion of mechanically sensitive tissues (e.g., visceral pain) or nerve blockage and injury (e.g., neuropathic pain). Tumors contain cells of the immune system, which release factors such as endothelial vasoconstrictor peptides, prostaglandins, and tumor necrosis factor alpha (TNF-alpha) that agitate or sensitize primary afferent nerves to peripheral injurious stimuli. Persistent pain induces central sensitization and persists as neuropathic pain due in part to central sensitization. Protein hydrolases produced by tumor cells can damage sensory and sympathetic nerve fibers, causing neuropathic pain. 3.Bone pain induced by metastatic cancer: Injury or infiltration of sensory neurons throughout and innervating bone marrow can cause pain. Normal bone transformation is altered, and the regulatory mechanism that balances bone-breaking and bone-forming activities is out of order. In advanced disease, bone loses mechanical strength and is susceptible to osteolysis, pathologic fractures, and microfractures. Mechanical distortion of the periosteum may be a major source of pain. 4. Neurological disorders: Neurological disorders associated with chemotherapy appear due to different mechanisms, including chemotherapeutic drug-induced disruption of microtubule protein function, which, along with the release of cytokines, leads to the degeneration of sensory neurons and the sensitization of afferent nerves to primary injurious stimuli. Radiation therapy can cause tissue fibrosis, nerve entrapment, and microvascular obstruction of the nerve. Nerve tissue entrapment or ulceration contributes to central sensitization.