Regarding the mechanism of cancer pain (cancerpain), it is believed that there are three pathways, namely: pain caused by cancer development, pain caused by diagnosis and treatment of cancer, and pain caused by infection, chronic painful diseases and cancer pain syndrome in cancer patients. Among these three pathways, 75% to 80% of patients are caused by tumor invasion into soft tissues, bone marrow and nervous system, 15% to 20% are caused during the diagnosis and treatment of cancer, and 5% to 10% are caused by the combination of painful diseases.
I. Pain caused by cancer development
1.Cancer invades nerve tissue
Cancer cells infiltrate through the lymphatic tract around the nerve sheath or along the weaker resistant parts around the nerve, and then invade to the nerve axon. Pain caused by cancer invasion of nerves has three causes.
(i) The nerve fibers within the nerve sheath are caused by infiltration of strangulation;
(2) Cancer cells release certain pain-causing substances, such as 5-hydroxytryptamine, bradykinin and histamine, which act on peripheral nerves and cause pain;
(3) The blood vessels that nourish the nerves are blocked by cancer cells, and the nerve fibers are in a state of ischemia, resulting in pain. Clinically, cancer metastasis produces intractable pain, often in the form of neuralgia, which is acute in nature and often radiates to the distribution of nerves on the body surface. When the cancer infiltrates into the abdominal plexus, mesenteric plexus and sacral plexus, the pain site becomes unclear and the pain is persistent.
2.Epidural metastasis and spinal cord compression
Epidural metastasis is a common complication of breast cancer, prostate cancer, lung cancer, multiple myeloma, malignant melanoma and kidney cancer. When epidural metastasis cancer compresses the spinal cord, the pain is confined to the conus, near the midline. When the tumor invades the nerve root, sharp pain or stabbing pain in the nerve root distribution area occurs, and the pain is distributed in a band. If left untreated, spinal cord compression syndrome may occur, accompanied by changes or disorders of sensation, movement and vegetative nerves.
3.Cancer invades the canal organ
When malignant tumor causes ductal organ dysfunction, it can produce pain, which is characterized by no clear localization, periodic and recurrent attacks, often accompanied by nausea, vomiting and abdominal distension. Biliary tract and pancreatic duct stenosis or obstruction often cause intense pain; uterine cancer and ovarian cancer compression and invasion of ureter can also cause intolerable colic.
4.Cancer invades the vascular system
Cancer can cause pain when it compresses, blocks or infiltrates arteries, veins and lymphatic vessels.
5.Cancer invades bone
Both primary bone tumor and metastatic bone tumor can produce intolerable pain.
6.Cancer
The pain is caused by the release of tumor necrosis factor, prostaglandin, 5-hydroxytryptamine, bradykinin, histamine and other pain-causing substances from necrotic disintegration of cancer cells.
II. Pain caused by cancer diagnosis and treatment
1.Diagnostic examination
Pain caused by bone marrow aspiration biopsy, lumbar puncture, various endoscopic examinations and other invasive examinations can bring pain to cancer patients.
2.After surgery
Painful surgical operations that damage nerves and postoperative scars that form tiny neuromas can cause pain; contracture and pulling of postoperative scars and recurrence of cancer tumors that pull tissues can produce pain.
3.After radiation therapy
Painful radiation therapy can cause fibrosis of tissues, compressing or pulling nerves and pain-sensitive tissues to produce pain. Common post-radiation therapy pain syndromes include radiation plexopathy and radiation myelopathy. In addition, mucositis, dermatitis, enteritis, herpes zoster and radiation pneumonia produced after radiotherapy can lead to the occurrence of pain.
4.After chemotherapy
Painful venipuncture during chemotherapy; diffuse abdominal pain caused by hepatic artery perfusion chemotherapy and intraperitoneal chemotherapy; phlebitis, mucositis, enteritis, hemorrhagic cystitis caused by chemotherapy; and polyneuritis caused by toxic side effects of chemotherapy drugs.
5.After interventional treatment
Pain can be caused by various percutaneous organ punctures (such as percutaneous hepatic puncture, percutaneous renal puncture, etc.); invasive interventional techniques such as percutaneous arteriovenous puncture placement, etc.
6, after hormone therapy
Pain after hormone therapy, also called steroidal pseudo-rheumatism, refers to the burning pain in muscles, tendons, joints and bones all over the body of cancer patients after receiving glucocorticoid therapy, especially spasmodic pain in intercostal muscles, accompanied by general discomfort, weakness and fever, and sometimes accompanied by psychological and mental disorders.
7.After immunotherapy
Pain commonly caused after immunotherapy refers to acute pain caused by interferon, which is manifested by fever, chills, myalgia, arthralgia and headache.
8.After analgesic treatment
Pain cancer pain patients in the course of analgesic treatment can also produce new pain. Intramuscular injection and subcutaneous injection of analgesics can cause pain; some patients can have recurrent full headache after using opioids, etc.
3. Co-infection, chronic pain disease and cancer pain syndrome
1.Pain caused by cancer co-infection Malignant tumor patients are very likely to have painful infections, which are often caused by bacteria, fungi or viruses.
2.Cancer combined with chronic pain disease refers to cancer patients suffering from various kinds of arthritis, fasciitis, cervical spondylosis, lumbar disc herniation, etc. at the same time.
3.Cancer combined with cancer pain syndrome refers to cancer patients with cancer pain syndrome, and pain with certain characteristics according to the location and tissue structure of tumor invasion. General treatment is relatively difficult and requires comprehensive treatment.
4.Psychological factors (uneasiness, anger, depression, etc.) are an important reason for increasing the pain level of cancer patients and hindering the effect of cancer pain treatment.