What is Cancer?
The body is composed of cells. Normally, cells are under the control of the body's mechanisms that regulate both their growth (proliferation) and location in the body. Cancer cells are abnormal cells. They fail to follow the body's rules for growth and localization. There are two basic properties of cancer cells. They defy the normal restraints for cell growth (a mass of abnormal cells is called a tumor), and they invade and take over areas of the body meant for other cells. These two properties make cancer cells both dangerous to the body and enable them to generate pain. The technical terms associated with cancer and cancer cells, as well as causes and types of cancer, are beyond the scope and purpose of this discussion.
What is Pain?
Pain is an unpleasant physical and emotional experience. It is one of the body's most important communication tools because it is a way to tell us something is wrong. Pain can have multiple causes, and it can last a brief period or persist for a long time. There are times when a person experiences pain without knowing the cause. Pain, regardless of whether the cause is known or unknown, can adversely affect a person's quality of life, as well as reduce their functional ability.
How Does Cancer Cause Pain?
There are a variety of mechanisms that may generate pain for cancer patients. Pain can be the result of cancer itself, the cancer tests and treatments, or all of these things.
As tumors grow and/or spread, they can press against the space they take up or destroy tissues (for example, internal organs) and/or nerves (like those that connect the brain and spinal cord or nerves in the arms or legs).
Diagnostic Test and Treatment-Induced Pain
- Diagnostic tests: Procedures like a biopsy or bone marrow test may cause pain depending on the location of the biopsy or test.
- Chemotherapy-induced pain: Some of the painful side effects of chemotherapy treatment may include mouth sores, diarrhea and nerve damage. Chemotherapy drugs may damage nerves (generally, nerves in the extremities like arms and legs). This type of nerve damage is called chemotherapy-induced peripheral neuropathy. The nerve damage may result in feelings of numbness, tingling, burning, or weakness in the extremities.
- Radiation-induced pain: Some of the painful side effects of radiation therapy may be the result of it damaging normal tissues that are close to the cancerous tissues. Specifically, radiation may damage the tissues that envelope and protect nerves or directly destroy tissue in the brain or spinal cord. Radiation-induced neuropathies can result in feelings of numbness, tingling, and burning in various locations of the body.
- Surgical procedures: Removal of a tumor (resection) may cause pain depending on the size and location of the tumor, as well the amount of normal tissue that must be removed along with the tumor.
Types of Cancer Pain
Pain is a complex phenomenon, and there are many ways to classify it. Two common ways pain can be classified is by length of time (acute vs. chronic/persistent pain) and by its pathophysiology (nociceptive vs. neuropathic pain).
- Acute Cancer Pain: This is generally characterized as having recent or sudden onset and a relatively short or limited duration. Acute cancer pain often has an identifiable cause (for example, a pinched nerve or compression of an internal organ).
- Chronic/Persistent Cancer Pain: This is lasting pain or pain that continues beyond the time expected for healing. Chronic cancer pain may not have an easily identifiable cause. It is often best described as persistent pain. This persistent pain may be continuous or recurring. Three and six months from the onset of pain are the two most used time points to divide acute from chronic pain.
Cancer pain can also be classified by the kind of damage that causes it (its pathophysiology). Pain due to tissue damage is a sharp, throbbing, or aching. A tumor compressing and/or invading an internal organ like the intestines could cause this type of pain. Pain due to nerve damage feels like numbness, pins and needles, and/or burning. The nerve damage may be in the brain, spinal cord or peripheral nerves (nerves in the rest of the body that send signals to the brain). A tumor in the spine that compresses and/or invades the spinal cord or surrounding nerves could cause this type of pain.
Complexity of Cancer Pain
Cancer patients may experience pain that is mild, severe or anything in between. Due to the complexity of cancer pain, it may not easily be categorized in an "either/or" sense. Cancer patients often experience multiple types of pain that are generated by multiple causes, including those that are totally unrelated to cancer. Pain may persist after all cancer treatments and procedures have ceased and body has healed.
Cancer Pain Treatment Options
Most cancer patients expect pain as part of the reality of living with and treating cancer. They, therefore, are hesitant to have continual discussions about their level of pain and discomfort with their treating physicians. Unfortunately, this mindset causes many patients to live with levels of pain that are unnecessary.
Treating cancer pain is complex and may require multiple treatment methods. Therefore, a physician specializing in the treatment of pain who is able to come up with an individual diagnosis and a holistic treatment plan should assess each patient's cancer pain.
Treatments for cancer pain involve both non-surgical and surgical options. Treatments for chronic cancer pain, regardless of the cause, are quite diverse. Surgical alternatives are a later course of treatment if other means have been exhausted. It is often necessary to utilize a combination of treatments.
- Pharmacotherapy: this includes both over-the-counter and prescription medications to treat swelling, inflammation and/or pain.
- Injections and nerve blocks: these are site-specific injections that deliver medications to decrease swelling, inflammation and/or pain.
- Additional options to treat cancer pain may include: acupuncture, psychological therapy, physical therapy, trigger point injections and nutritional therapy.
- Neurostimulation: a device is surgically implanted that delivers electrical signals to the spinal cord, brain or specific nerves. Basically, the electrical signals disrupt the pain signals being sent to the brain.
- Peripheral nerve stimulation: an electrode is placed along the course of a peripheral nerve (for example, sciatic, ulnar or median nerves) that may be the cause of pain, numbness or tingling.
- Spinal cord stimulation: a device is surgically implanted that delivers electrical signals to the spinal cord to disrupt pain signals.
- Deep brain stimulation / motor cortex stimulation: an electrode is implanted directly into the brain, which delivers an electrical stimulus to specific parts of the brain. The electrical stimulus disrupts pain signals from reaching a specific region of the brain.
- Targeted drug delivery to the central nervous system: this is delivery of medications directly to a specific site deep within the body versus taking a medication orally, intravenously or topically.
- Intrathecal drug delivery (also known as a pain pump): A pump is surgically implanted under the skin, and it delivers medication (for example, opioids or anesthetics) directly into the cerebral spinal fluid (CSF).
- Intraventricular drug delivery: Medication is injected directly into a specific portion of the brain (called a ventricle). Alternatively, an implantable pump can be used.
- Neuroablation / radio frequency (RF) ablation: these procedures use radio waves to deactivate a specific part of the nerve, spinal cord or brain that is causing pain.
- Spinal cord ablation: Radio waves are used to deactivate specific portions of the spinal cord. Examples of spinal cord ablation procedures include cordotomy, myelotomy, and dorsal root entry zone lesion.
- Peripheral nerve ablation: Radio waves are used to deactivate specific portions of a peripheral nerve (for example, sciatic, ulnar or median nerves) that may be the cause of pain, numbness or tingling. Examples of peripheral nerve ablation procedures include rhizotomy and sympathectomy.
- Brain and Brainstem ablation: Radio waves are used to deactivate specific portions of the brain or brainstem that may be the cause of pain. An example of a brainstem ablation procedure is a tractotomy. Examples of brain ablation procedures include thalamotomy, cingulotomy, and hypophysectomy.