The incidence of cancer worldwide is 18 million cases per year.
- 55% of patients undergoing cancer treatment experience pain .
- Despite improvements in early detection and treatment of cancer, advances related to cancer pain management have mostly been inadequate. 
- Cancer pain remains a major problem and affects quality of life . It includes physical, psychosocial-emotional and spiritual components .
- Barriers to effective cancer pain management remain. There is a general lack of knowledge among practitioners regarding the assessment and management of cancer pain .
- Pain in cancer patients may be caused by direct tumor involvement in diagnostic or side effects of therapeutic procedures or by toxicity of cancer therapy. 
Types of Pain
The type of pain  determines the type of medication or treatment.
- Acute Pain: Acute pain is severe, comes on quickly, and lasts relatively short time.
- Chronic Pain: Chronic pain can last for a long time. Pain that lasts 3 months or more is usually considered chronic. If not treated properly, it can disrupt your life and normal activities.
- Breakthrough pain: Breakthrough pain is an unpredictable, sudden onset of pain that can occur even when patients are taking conventional pain medication for chronic pain. It “breaks through” the pain relief of conventional painkillers; it comes on quickly, lasts longer, and feels like chronic pain Except it’s worse and can vary in intensity. It can be treated with additional or another pain medication.
Causes of Cancer Pain
It is caused by stress or trauma to the somatosensory system. It can lead to loss of function, increased pain sensitivity, and spontaneous pain. Neuropathic pain is common in cancer and is often chronic, either persistent or characterized by recurrent pain . Research Indicating a higher prevalence of 40%. 
Damage by primary tumor or metastases
It may be due to direct infiltration or metastasis of the primary tumor to peripheral or central nervous system components. Examples include thoracic tumors that invade the brachial plexus or abdominal or pelvic tumors that affect peripheral nerves that invade the lumbosacral plexus system. Or bone metastases involving the central nervous system leading to vertebral body collapse leading to spinal cord compression .
Damage due to the treatment
Neuropathic pain from cancer treatment can result from side effects or complications of cancer treatment: surgery (direct trauma to peripheral nerves), radiation therapy, and chemotherapy .
Interventions commonly associated with posttraumatic neuropathic pain syndrome include mastectomy and thoracotomy . Postmastectomy pain syndrome is a chronic neuropathic pain affecting the inner axillary breast and chest wall after breast cancer surgery .
It can cause chronic painful radiation-induced neuropathy. Delayed localized damage to the nervous system from radiation therapy is common, sometimes manifesting months or even years after treatment. Due to radiation-induced nerve compression, which is usually progressive and irreversible Fibrosis or direct nerve and vascular injury due to microvascular changes .
Chemotherapy-Induced Peripheral Neuropathy (CIPN)
It is a common painful dose-dependent and dose-limiting side effect of chemotherapy. CIPN is caused by direct neurotoxic effects of chemotherapy on dorsal root ganglion neurons or their axons, resulting in loss of sensation in the stocking-glove distribution and pain in sensory ataxia. pain is often Described as stinging or burning or “electric shock.” Spontaneous movements and occasional cranial nerve involvement are less common. Symptoms usually appear during the first two months of treatment and worsen as treatment progresses, then stabilize soon after discontinuation treat. However, symptoms may persist long after treatment. Common neurotoxic chemotherapeutic agents include taxanes (paclitaxel and docetaxel), platinum agents (cisplatin and oxaplatin), vinca alkaloids (vincristine), thalidomide, and proteasome inhibitors ( Bortezomib) .
Eighty percent of bone cancer metastases arise from breast, lung, and prostate cancer. The relative incidence of bone metastases is 65-75% in breast cancer 65-75% in prostate cancer 60% in thyroid cancer 40% in bladder cancer 20-25% in renal cell carcinoma 14 in renal cell carcinoma -45% melanoma. 65% of bone metastases arise from breast cancer (women) and prostate cancer (men). The remaining 35% of metastases are from kidney, thyroid, and lung cancers .
Patients initially experience intermittent, dull pain that becomes persistent and more severe as the disease progresses. Its intensity cannot be determined by tumor type, tumor size, number of metastases, or bone involvement. Pain is located near the bone metastases. Pain worsens with increased nocturnal activity. May be accompanied by fever .
Orofacial pain (OFP) may be caused by direct cancer involvement of anatomical structures, side effects of cancer treatment, or patient comorbidities. About half of head and neck cancer patients report OFP before tumor treatment 81% during treatment 70% at the end of treatment and 36% 6 months after treatment .
Causes of OFP
- Oral mucositis and stomatitis are common acute adverse effects of combination chemotherapy and radiation therapy (CRT). Severe mucositis occurs in 60% to 90% of cases and can significantly increase pain during anticancer treatment .
- Temporomandibular disorders (TMD) frequently affect patients with HNC. Trismus, a TMD caused by damage to the muscles of mastication, is a late complication of radiotherapy to the head and neck .
- Burning mouth syndrome (BMS) and painful posttraumatic trigeminal neuropathy Chronic neuropathy characterized by unilateral or bilateral oral burning pain on the tongue and other parts of the oral mucosa may be due to nerve damage caused by CRT .
Phantom phenomena consist of three distinct elements :
- Phantom Limb Pain (PLP): Painful sensations associated with amputation.
- Phantom Limb Sensation (PLS): Sensation other than pain associated with amputation.
- Stump Pain (SP): Pain limited to the amputation stump.
Studies have shown that phantom limb pain after cancer-related amputation in children and young adults is common but transient in most patients .
Pain Mechanisms in Cancer Pain
The following pain mechanisms are considered in cancer pain:
Central sensitization mechanisms: Spontaneous or persistent “pain” indicates a central pain mechanism. Increased sensitivity of higher order neurons in the central nervous system elicits pain in the absence of peripheral nociceptive stimuli .
Peripheral Sensitization Mechanisms: Pain is caused by primary lesions or dysfunctions in the peripheral nervous system (PNS). Cancer-related: Brachial plexopathy Chemotherapy-induced neuropathy Cranial neuropathy Post-radiation plexopathy and surgical neuropathy. 
Sympathetic pain : Cancer pain is associated with over- or under-activation of the sympathetic nervous system. Sympathetic dependent pain (SDP) or sympathetic maintenance pain (SMP) is characterized by cutaneous dysesthesia with sympathetic hyperactivity.
- Allodynia (pain caused by a nonnoxious stimulus, usually tested by light touch), hyperalgesia (delayed pain response to a touch stimulus), and hypoalgesia with “burning” and “burning” on pinprick testing of painful areas throbbing” feeling.
- Signs of excessive sweating and vasoconstriction (pale, cold white extremities) suggest sympathetic overactivity; more common in the lower extremities, chest, and neck, and less often in the upper extremities.
Nociceptive Mechanisms: Nociceptive pain in cancer patients may result from disuseful adaptations and abnormal movements or postures adopted by cancer patients. 
Cognitive-affective mechanisms: Patients with cancer pain show higher levels of anxiety and depression. Cognitive-affective dysfunction in cancer pain may be due to cancer or disease-related treatments, such as prescribed narcotics and opioids .
Barriers to adequate pain management
Despite new pain management and pain management guidelines, some patients are not being treated appropriately. Barriers to proper pain management may arise from :
- Barriers related to healthcare professionals: lack of knowledge and skills to assess pain problems, and physician reluctance to prescribe opioids to patients.
- Patient-Related Barriers: Cognitive and Affective Factors and Adherence to Analgesic Protocol.
- System-related barriers: Limited access to opioids and the availability of pain and palliative care specialists pose additional challenges, especially in under-resourced settings.
The National Comprehensive Cancer Network (NCCN) has developed guidelines for the assessment and management of cancer-related pain in the adult oncology population. A comprehensive pain assessment includes assessment of pain intensity, etiology and pathophysiology of pain, and identification of the patient’s cause of pain Determined as target pain score or functional outcome .
Clinicians should take an appropriate pain history. He/she should ask the patient about the pattern of pain scores (high/low/average) and the effect of analgesics on pain over time, rather than focusing only on pain at the time of assessment .
The intensity of pain can be measured by :
- Cognitively intact patients may be able to rate pain on a numerical rating scale from 0 (no pain) to 10 (worst pain imaginable). Alternatively, some patients may be prescribed a categorical scale or a visual analog scale (no pain, mild pain, moderate pain, or severe pain).
- Patients with cognitive decline may not provide a verbal pain history, but can provide information that can guide a treatment plan. Clinicians should look for nonverbal signs of discomfort (eg, agitation, restlessness, restlessness, grimacing, or confusion). verbal but with Impaired memory may not provide a reliable pain history of how they felt in the past, so providers need to focus on pain levels reported during sessions. Patients with severe cognitive impairment may not exhibit characteristic behavioral responses to pain. In these cases, clinicians should use Their judgment is to consider whether cognitively intact patients with a similar disease burden would report pain, and if so, clinicians should initiate a symptomatic treatment plan and monitor response. Clinicians should not assume the absence of pain just because a patient does not have pain A classic oral history of pain could not be provided.
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