Most patients with advanced cancer and up to 60% of patients with any stage of the disease experience significant pain. The World Health Organization (WHO) estimates that 25% of all cancer patients die with unrelieved pain. The cause of cancer pain should be treated whenever possible. By doing so, one can frequently achieve rapid, lasting pain relief and may prevent the problems associated with untreated progressive disease, such as spinal cord compression and pathologic fracture. Also, the need for pain medications may be diminished, thus reducing side effects and drug interactions. In most cancer patients, pain can be relieved adequately, and yet it is undertreated for a multitude of reasons. The problem is not trivial, as unrelieved pain is known to be a risk factor for suicide in cancer patients. Current efforts are being directed toward standardizing pain treatment and separating issues of pain treatment from those of substance abuse. The effective management of cancer patients with pain is best accomplished with coordination of the services of multidisciplinary professionals, community volunteers, and the family. Pathophysiology Pathophysiologic classification of pain forms the basis for therapeutic choices. Pain states may be broadly divided into those associated with ongoing tissue damage (nociceptive) and those resulting from nervous system dysfunction in the absence of ongoing tissue damage (non-nociceptive or neuropathic). Damage to the nervous system may result in pain in an area of altered sensation. Such pain is typically described as burning or lancinating. Patients may report bizarre complaints, such as painful numbness, itching, or crawling sensations. The postamputation phenomenon of phantom pain (pain referred to the lost body part) may be disabling. Psychological factors Psychological factors may affect the reporting of pain. Chronic unrelieved pain has psychological consequences, but this does not support a psychiatric basis for the pain complaint. "Psychogenic pain" or somatoform pain disorder is rare in cancer patients. Pain syndromes Cancer pain syndromes vary by tumor type and are related to patterns of tumor growth and metastasis. Pain may also be related to antineoplastic therapy or may be unrelated to either the neoplasm or its treatment. Elements of management Elements of cancer pain management include a proper medical evaluation, psychosocial assessment, formulation of the pain "diagnosis," and consideration of pharmacologic and nonpharmacologic treatments. Ongoing care is needed to monitor the efficacy of analgesics and the evolution of different symptoms during treatment or disease progression. The steps in medical decision-making are to:

• determine whether primary antineoplastic therapy is indicated for palliation
• tailor pharmacologic analgesic therapy to individual needs
• consider concurrent nonpharmacologic analgesic methods
• monitor response and modify treatment accordingly (Figure 1).

The patient is the focus of care, although family members and others often participate in treatment decisions and require emotional support. Medical evaluation
Pain history Begin with a thorough history. As there are no objective means with which to verify the presence of pain, one must believe a patient's complaint. The physiologic signs of acute pain-elevated blood pressure and pulse rate-are unreliable in subacute or chronic pain. Most cancer patients report more than one site of pain. A detailed history of each type of pain should be elicited (Table 1). As the chief complaint resolves, what was initially a secondary problem may require attention. Pain-rating scales should be used to establish a baseline against which the success of treatment may be judged (Figure 2). Behavioral observations may be used to assess patients who are unable to communicate. Although there are standardized tools for preverbal children, they are not available for impaired adults. Thus, it is sometimes necessary to treat pain presumptively. Physical examination includes careful neurologic testing, especially if neuropathic pain is suspected. Pain in an area of reduced sensation, allodynia (ie, when normal stimuli are reported as painful), and hyperpathia or summation of painful stimuli indicate a neuropathic process. The assessment should evaluate the putative mechanisms that may underlie the pain. Review of disease extent and current conditions The extent of disease and current medical conditions must be determined. Diagnostic tests should be reviewed and supplemented as necessary. Treatment and drug history Cancer treatment and prior analgesic interventions, along with their outcomes, should be recorded. Psychological dependency on any drug, including alcohol(Drug information on alcohol), must be identified. Psychosocial assessment
To establish trust, the evaluating clinician should explore with the patient the significance of the pain complaint. The impact of pain and other symptoms on functional status must be understood to establish treatment goals. Suffering may be attributable to many factors besides physical complaints. The clinician should ask about such psychological factors as financial worries, loss of independence, family problems, social isolation, and fear of death. Often, cancer patients meet diagnostic criteria for the psychiatric diagnosis of adjustment disorder with anxiety and/or depressed mood. Patient subgroups To help define therapeutic goals, the patient's age and prognosis may be considered. Adjustments in drug doses are usually needed for elderly patients, who are more sensitive to analgesics and their side effects. Adolescents may require relatively larger doses of opioids. Pain in children is underreported and should be specifically elicited using age-appropriate assessment tools.