The cancer pain involves complex pathophysiology. Cancer pain when caused by malignant tumor is often serious condition. Pain caused by benign tumor is also a serious medical condition, but may not be life threatening. Cancer pain is nociceptive pain in the initial phase and in the later phase becomes mixed pain. Mixed pain consists of nociceptive and neuropathic cause and symptoms.
Types of Cancer
- Cancer tissue mass enlarges in size, but does not infiltrate into the surrounding tissue.
- Does not Metastasize in distant or adjacent organs or tissue.
- Tumor size could be massive and may cause erosion of surrounding normal tissue resulting in pressure and ischemia.
- Pressure on nerve causes symptoms like pain, tingling and numbness.
- Massive size also causes pressure on surrounding tissue and organs results in ischemic changes. Ischemia causes lack of blood supply to normal tissue. These changes occur secondary to pressure and compression of blood vessels.
- Ischemic tissue may end up necrotic and lead to symptoms such as nausea, vomiting, dizziness and bleeding.
- Some time massive size of benign tumor can cause obstruction of organs followed by constipation and retention of urine or stool.
- This type of cancer spreads to surrounding and distant tissues as well as organs. Spread is commonly observed through blood or lymphatic.
- Distant spread is metastasis and observed with spread of cancer cells into distant organs through blood or lymphatics.
- Cancer tissue may spread to liver, brain and lungs through blood vessels and lymphatics.
- Tumor tissue mass is called metastasis when spread into other distant organs.
- Local cancer tissue spread involves increase of size as well as penetration and infiltration of surrounding normal tissue or organs.
- Penetration of cancer tissue into blood vessel causes ischemia by obstruction to flow and bleeding by tear or rupture of blood vessels. Tear or rupture follows life threatening major or minor bleeding.
Causes of Cancer Pain Which Indicates Serious Medical Condition
- Inflammation of cancer cells and surrounding tissue
- Pinch or compression of the surrounding nerve
- Irritation of pain receptors
- Infiltration and pressure from cancer tumor growth causes ischemic pain of surrounding tissue.
- Visceral pain becomes serious when viscera is obstructed resulting in severe nausea, vomiting and constipation.
- Pressure or invasion on surrounding sympathetic and somatic pain nerves.
- Side effects from chemotherapy such as peripheral neuropathy.
- Radiation therapy causes inflammation, tissue necrosis, tissue injuries and scarring. Inflamed tissue heals with scarring. Scar tissue may encroach upon the nerve causing severe pain.
- Ischemic pain secondary to obstruction of blood vessels causing poor circulation.
- Bone fracture and metastasis.
- Infection and abscess formation of ischemic surrounding tissue
Types of Mixed Cancer Pain
- Irritation of Pain Receptors- Pain receptors generated pain impulses when stimulated by above average threshold of pressure, temperature or chemicals.
- Pinching of peripheral nerve fibers
- Local inflammation causes nociceptive pain through the release of prostaglandins, substance P, serotonin, histamine, acetylcholine, and bradykinin.
- Neuropathic pain results from pathophysiological changes at the peripheral or central nervous system.
- Peripheral nervous system changes results in hypersensitive pain receptors and nerve fibers.
- The changes to the peripheral nervous system are caused by trauma, distortion, cancer treatment (chemotherapy or radiation therapy).
- Central nervous system changes results in hypersensitive spinal neurons and abnormal secretions of neurotransmitters in spinal cord and brain.
- Prolonged pain or inadequately treated pain promotes the abnormal physiological changes in central nervous system.
- A variety of neurotransmitters modulate pain sensations at the level of the synapses.
- Some of the neurotransmitters are serotonin, noradrenalin, prostaglandins, substance P, endorphins, and enkephalins.
- These neurotransmitters are active at the level of the nociceptors and at the level of the spinal cord and the brain.
Classification And Types Of Cancer Pain
Acute Cancer Pain
- Lasts less than 6 months- Mostly seen in benign cancer tumor. Pain is less intense once benign cancer tumor is removed by surgery.
- Pain is nociceptive in nature.
- Detailed investigation of acute pain helps to achieve early diagnosis of cancer.
- Example of Early Acute Pain- Bone cancers or testicular cancer are predominantly presented with early pain.
Chronic Cancer Pain
- Chronic pain is continuous pain, lasting more than 6 months.
- Pain is mixed in nature
Regional Cancer Pain
- Regional Serious Pain– Symptoms are observed because of tumor mass pressing on soft tissue, bones or nerves. Pain intensity depends on direct contact with nerve and nerve receptors.
- Visceral Serious Symptoms– Serious symptom is caused by advanced cancer. Chronic cancer pain becomes serious following cancer tissue encroaching and penetrating within normal organs, nerves and nervous system. Permanent destruction of nerves to bladder and intestine initiates loss of control on bladder (bladder incontinence and retention) or bowel function (bowel incontinence and retention).
- Cervical Pain– Cervical (neck) spread of cancer within cervical and brachial plexus may cause symptoms in neck and upper extremities. In cervical spinal cord compression, symptoms such as numbness and weakness may be wide spread causing monoplegia involving only one limb or paraplegia involving both limbs of upper or lower extremities or in few cases quadriplegia. Intensity of pain increases with certain commotions such as coughing or sneezing. These physiological disturbances cause pressure changes in spinal canal. Activities or movement of vertebral column such as flexion, extension or lateral rotation can also trigger severe intractable pain. Continuous pressure on sensory and motor nerve ultimately results in permanent nerve damage.
- Headache– Initial acute headache not responding to analgesics could be a sign of brain tumor or brain metastasis.
- Back Pain– Backache is often observed in cancer of the colon, rectum, or ovary with or without metastasis of vertebrae.
- Bone Pain: Cancer tissue may spread into skeletal system. Skeletal spread may be local or distant. Distant spread within skeletal system is caused by blood or lymphatic spread in metastatic cancer. Example: Lung cancer in advanced stage may spread locally into ribs or to distant skeletal system such as extremities into femur and humerus bone. Pancreatic and abdominal cancer can spread to vertebrae. Cancer that has spread into bones causes osseous pain and also occasional fracture. Fracture of bones itself can cause severe pain.
Serious Cancer Pain Following Spinal Cord Compression:
- Nerves come out of spinal canal from right and left side through transverse foramina. Primary or metastatic cancer cells can spread into spinal canal through transverse foramina.
- Serious pain is observed when malignant cancer tissue spreads into spinal canal either by triggering bony metastasis of vertebral body or by the developing growth within the spinal canal.
- Metastasis of spinal cord occurs through spread by lymphatics and/or blood.
- Most common cause of spinal cord compression is metastatic tumor mass of vertebral body overrunning the anterior half of spinal cord.
- It may also spread through supplementary bones of vertebrae into spinal canal and spinal cord.
- Spinal cord spread causes compression of spinal cord and nerves.
- Dermatomal spread of serious cancer pain depends on the segment of spinal cord compressed by primary or metastatic tumor.
Post Surgical Cancer Pain Which Could Be Serious in Nature:
- Surgical treatment may include excision of tumor mass and /or excision of metastasis tissue. Surgery could be biopsy or extensive operation causing substantial tissue trauma involving several dermatome segments of spinal cord.
- Surgery pain is acute and nociceptive.
- Pain felt by patient is enormous and diverse than cancer pain, but severity may be considerably complex and intractable.
- Resistance and tolerance to pain medication may set a challenge to treat postsurgical pain.
- Procedures related to cancer pain such as biopsies, blood draws, lumbar punctures, laser treatments etc. can cause pain.
- Phantom Pain: It is a neuropathic pain caused by excision of the nerve. It is commonly observed in an amputated limb and mastectomy. Phantom pain is difficult to treat. Phantom pain results in neuropathic complex regional pain syndrome.
Metastasis Cancer Pain
- Advanced aggressive cancer associated with metastasis is fatal and gives limited time.
- The life span can be prolonged for weeks to months after cancer treatment.
- Periodic check up of urine, blood, sputum and stool can be helpful in early diagnosis.
- Cancer patients with rapid growing malignant cancer may not survive for more than 6 months.
- Cancer is the second most common cause of death after heart disease. Cancer can be cured in few cases depending on early diagnosis and aggressive treatment.
- Non-aggressive cancer can give a lifetime of over 5 years in some cases after extensive therapy.
Cancer Pain Caused by Chemotherapy
- Severe pain is also observed after chemotherapy.
- Chemotherapy complication are Mouth sores (mucositis), Peripheral neuropathy (numb and painful sensations in the feet, legs, fingers, hands and arms), Constipation, diarrhea , nausea , and vomiting and abdominal cramps.
- Some people also experience bone and joint pain.
- Risk of infection after chemotherapy increases as immunity is compromised in pain and infection.
Risk Factors of Serious Cancer
Cancer Due to Chemical or Toxic Compound Exposures
Benzene, asbestos, nickel, cadmium, vinyl chloride, benzidine, N-nitrosamines, tobacco or cigarette smoke (contains at least 66 known potential carcinogenic chemicals and toxins), and aflatoxin.
Cancer Due to Ionizing Radiation
Uranium, radon, ultraviolet rays from sunlight, radiation from alpha, beta, gamma, and X-ray-emitting sources.
Cancer Due to Pathogens
Human papillomavirus (HPV), EBV or Epstein-Barr virus, hepatitis viruses B and C, Kaposi’s sarcoma-associated herpesvirus (KSHV), Merkel cell polyomavirus, Schistosoma spp., and Helicobacter pylori; other bacteria are being researched as possible agents.
A number of specific cancers have been shown linked to human genes. E.g. Breast cancer, ovarian cancer, colorectal cancer, prostate cancer, skin cancer and melanoma.