The problem of pain among cancer patients is endemic. Appropriate and effective clinical responses to this problem require that the physician appreciate the cause of the pain, its underlying mechanism, its natural history, and its significance.
A woman with breast cancer, who presents with shoulder pain, may have one of a number of pain syndromes, including postoperative frozen shoulder, paclitaxel(Drug information on paclitaxel) (Taxol)- or bisphosphonate-associated proximal myalgias, radiation or malignant upper brachial plexopathy, metastases in the bony structures of the shoulder, impending fracture of the proximal humerus, C4 radiculopathy associated with epidural encroachment or leptomeningeal metastases, hepatic capsular distension, or a benign pathology unrelated to the cancer. To arrive at an appropriate therapeutic plan, the treating clinician must be aware of the range of possible causes of the pain, their distinguishing clinical features, and the efficient diagnostic strategies available to isolate the specific cause as quickly and easily as possible. A lack of awareness of the range of diagnostic possibilities may result in undertreatment, overtreatment, or sometimes even inappropriate treatment of the pain.
Since the seminal works of John Bonica, various attempts have been made to taxonomize cancer pain.[2-5] A taxonomy is a clinically useful classification of a recognized clinical diversity. By necessity, taxonomies of this ilk must be open to reevaluation as knowledge and experience expands.
International Survey of Cancer Pain
In this article, Dr. Caraceni expands this process of taxonomic reevaluation based on his experience and the data accrued from an international survey of cancer pain characteristics and syndromes. This survey of pain-related data from 1,095 patients provided an unparalleled picture of the pain experience of cancer patients. Almost one-quarter of the patients experienced two or more pains; 93% had one or more pains caused directly by the cancer, and 21% had one or more pains caused by cancer therapies. When classified by pain mechanism, nociceptive pains due to somatic injury were the most common (71%). These were usually caused by bone or joint lesions (42%) or soft-tissue infiltration (28%). Pain generated by neuropathic pain mechanisms, such as peripheral nerve injuries, and visceral pain syndromes each occurred in 30% to 40% of patients.
Aside from identifying points of common understanding, the survey also identified a lack of convergent understanding regarding the concept of "breakthrough pain." Among clinicians from various countries reporting their experiences, there were large differences in the frequency with which breakthrough pain was diagnosed. This observation suggests the need for an improved understanding of this phenomenon.
Taxonomy of Pain Syndromes