Pain in cancer may arise from a tumor compressing or infiltrating nearby body parts; from treatments and diagnostic procedures; or from skin, nerve and other changes caused by a hormone imbalance or immune response. Most chronic (long-lasting) pain is caused by the illness and most acute (short-term) pain is caused by treatment or diagnostic procedures. However, radiotherapy, surgery and chemotherapy may produce painful conditions that persist long after treatment has ended.
The presence of pain depends mainly on the location of the cancer and the stage of the disease. At any given time, about half of all people diagnosed with malignant cancer are experiencing pain, and two-thirds of those with advanced cancer experience pain of such intensity that it adversely affects their sleep, mood, social relations and activities of daily living.
With competent management, cancer pain can be eliminated or well controlled in 80% to 90% of cases, but nearly 50% of cancer patients in the developed world receive less than optimal care. Worldwide, nearly 80% of people with cancer receive little or no pain medication. Cancer pain in children and in people with intellectual disabilities is also reported as being under-treated.
Guidelines for the use of drugs in the management of cancer pain have been published by the World Health Organization and others. Adequate pain management may sometimes slightly shorten a dying person's life.
Pain
Pain is classed as acute (short term) or chronic (long term). Chronic pain may be continuous with occasional sharp rises in intensity (flares), or intermittent: periods of painlessness interspersed with periods of pain. Despite pain being well controlled by long-acting drugs or other treatment, flares may occasionally be felt; this is called breakthrough pain, and is treated with quick-acting analgesics.
The majority of people with chronic pain notice memory and attention difficulties. Objective psychological testing has found problems with memory, attention, verbal ability, mental flexibility and thinking speed. Pain is also associated with increased depression, anxiety, fear and anger. Persistent pain reduces function and overall quality of life, and is demoralizing and debilitating for the person experiencing pain and for those who care for them.
Pain's intensity is distinct from its unpleasantness. For example, it is possible through psychosurgery and some drug treatments, or by suggestion (as in hypnosis and placebo), to reduce or eliminate the unpleasantness of pain without affecting its intensity.
Sometimes, pain caused in one part of the body feels like it is coming from another part of the body. This is called referred pain.
Pain in cancer can be produced by mechanical (e.g. pinching) or chemical (e.g. inflammation) stimulation of specialized pain-signalling nerve endings found in most parts of the body (called nociceptive pain), or it may be caused by diseased, damaged or compressed nerves, in which case it is called neuropathic pain. Neuropathic pain is often accompanied by other feelings such as pins and needles.
The patient's own description is the best measure of pain; they will usually be asked to estimate intensity on a scale of 0–10 (with 0 being no pain and 10 being the worst pain they have ever felt). Some patients, however, may be unable to give verbal feedback about their pain. In these cases one must rely on physiological indicators such as facial expressions, body movements and vocalizations such as moaning.
Cause
About 75 percent of cancer pain is caused by the illness itself; most of the remainder is caused by diagnostic procedures and treatment.
Tumor-related Tumors cause pain by crushing or infiltrating tissue, triggering infection or inflammation, or releasing chemicals that make normally non-painful stimuli painful.
Invasion of bone by cancer is the most common source of cancer pain. It is usually felt as tenderness, with constant background pain and instances of spontaneous or movement-related exacerbation, and is frequently described as severe. Rib fractures are common in breast, prostate and other cancers with rib metastases.
The vascular (blood) system can be affected by solid tumors. Between 15 and 25 percent of deep vein thrombosis is caused by cancer (often by a tumor compressing a vein), and it may be the first hint that cancer is present. It causes swelling and pain in the legs, especially the calf, and (rarely) in the arms. The superior vena cava (a large vein carrying circulating, de-oxygenated blood into the heart) may be compressed by a tumor, causing superior vena cava syndrome, which can cause chest wall pain among other symptoms.
When tumors compress, invade or inflame parts of the nervous system (such as the brain, spinal cord, nerves, ganglia or plexa), they can cause pain and other symptoms. Though brain tissue contains no pain sensors, brain tumors can cause pain by pressing on blood vessels or the membrane that encapsulates the brain (the meninges), or indirectly by causing a build-up of fluid (edema) that may compress pain-sensitive tissue.
Pain from cancer of the organs, such as the stomach or liver (visceral pain), is diffuse and difficult to locate, and is often referred to more distant, usually superficial, sites. Invasion of soft tissue by a tumor can cause pain by inflammatory or mechanical stimulation of pain sensors, or destruction of mobile structures such as ligaments, tendons and skeletal muscles.
Pain produced by cancer within the pelvis varies depending on the affected tissue. It may appear at the site of the cancer but it frequently radiates diffusely to the upper thigh, and may refer to the lower back, the external genitalia or perineum.
Diagnostic procedures Some diagnostic procedures, such as lumbar puncture (see post-dural-puncture headache), venipuncture, paracentesis, and thoracentesis can be painful.International Association for the Study of Pain Treatment-Related Pain
Treatment-related
Potentially painful cancer treatments include: immunotherapy which may produce joint or muscle pain; radiotherapy, which can cause skin reactions, enteritis, fibrosis, myelopathy, bone necrosis, neuropathy or plexopathy; chemotherapy, often associated with chemotherapy induced peripheral neuropathy, mucositis, joint pain, muscle pain, and abdominal pain due to diarrhea or constipation; hormone therapy, which sometimes causes pain flares; targeted therapies, such as trastuzumab and rituximab, which can cause muscle, joint or chest pain; angiogenesis inhibitors like bevacizumab, known to sometimes cause bone pain; surgery, which may produce post-operative pain, post-amputation pain or pelvic floor myalgia.
Infection The chemical changes associated with infection of a tumor or its surrounding tissue can cause rapidly escalating pain, but infection is sometimes overlooked as a possible cause. One study found that infection was the cause of pain in four percent of nearly 300 people with cancer who were referred for pain relief. Another report described seven people with cancer, whose previously well-controlled pain escalated significantly over several days. Antibiotic treatment produced pain relief in all of them within three days.
Management Cancer pain treatment aims to relieve pain with minimal adverse treatment effects, allowing the person a good quality of life and level of function and a relatively painless death. Though 70–90 percent of cancer pain can be eliminated or well controlled, a 2022 review found roughly one in five of people with cancer pain included in the analysis received less than optimal care. This fraction is highly variable and tends to be higher in countries of lower gross national income.
Cancer changes over time, and pain management needs to reflect this. Several different types of treatment may be required as the disease progresses. Pain managers should clearly explain to the patient the cause of the pain and the various treatment possibilities, and should consider, as well as drug therapy, directly modifying the underlying disease, raising the pain threshold, interrupting, destroying or stimulating pain pathways, and suggesting lifestyle modification. The relief of psychological, social and spiritual distress is a key element in effective pain management.WHO guidelines:
A person whose pain cannot be well controlled should be referred to a palliative care or pain management specialist or clinic.
Psychological Vulnerabilities
To attempt psychological treatment for cancer pain, medical staff may seek to understand certain vulnerabilities that might predispose certain patients to mental disorders exacerbated by their diagnosis and the physical pains often associated with it. Oncological research has found a significant interplay between psychological vulnerabilities and physical cancer pain in postoperative cancer patients, implying that these two factors are uniquely- and yet also simultaneously- a potential part of the cancer pain experience. Psychological vulnerabilities such as anxiety or depression present in patients before cancer operations correlate with higher pain levels after said operations across several research studies, yet others find that these diagnoses sometimes only emerge after these treatment conditions. Use of antidepressants before cancer diagnosis is also associated with greater chronic pain post operation.
Certain sociodemographic characteristics have also been shown to disproportionately affect the types of people who are more likely to experience mental health issues due to cancer diagnoses. Psycho-oncology researchers repeatedly find that 35-40% of people with cancer have some sort of mental disorder that could be clinically diagnosed, suggesting that mental health issues often coincide with cancer diagnoses in such a way that psychological pain in itself can be considered a cancer pain. It is well-noted that depression and anxiety are significantly correlated with cancer diagnoses, which are mental health disorders disproportionately experienced by female cancer patients and people who live in rural areas. Many women with breast cancer who undergo surgical procedures experience chronic breast pain that can last upwards of years, contributing not only to the experience of physical pain but also to decreased mental health and quality of life.
Coping strategies The way a person responds to pain affects the intensity of their pain (moderately), the degree of disability they experience, and the impact of pain on their quality of life. Strategies employed by people to cope with cancer pain include enlisting the help of others; persisting with tasks despite pain; distraction; rethinking maladaptive ideas; and prayer or ritual.
Some people in pain tend to focus on and exaggerate the pain's threatening meaning, and estimate their own ability to deal with pain as poor. This tendency is termed "catastrophizing". The few studies so far conducted into catastrophizing in cancer pain have suggested that it is associated with higher levels of pain and psychological distress. People with cancer pain who accept that pain will persist and nevertheless are able to engage in a meaningful life were less susceptible to catastrophizing and depression in one study. People with cancer pain who have clear goals, and the motivation and means to achieve those goals, were found in two studies to experience much lower levels of pain, fatigue and depression.