Cancer pain, pathophysiology, characteristics and syndromes.

In this study the pathophysiology and characteristics of cancer pain together with cancer pain syndromes and guidelines of management are reviewed. Tumour-associated pain may be nociceptive (somatic or visceral) if the sustaining mechanisms are related to ongoing tissue pathology, or neuropathic when pain is associated with injury to neural tissues. The mechanism by which tumours produce pain include obstruction of lymphatic and vascular channels, distension of a hollow viscous, oedema and tissue inflammation or necrosis. Injury to tissues results in the local release of numerous chemicals that mediate transmission of pain stimulus. Cancer pain syndromes result from one or more of three fundamental causes; direct tumour involvement of tissues, cancer-directed therapy, and mechanisms unrelated to cancer or its treatment. Cancer pain syndromes are also classified as acute or chronic. Cancer pain characteristics provide some of the data essential for syndrome identification. These characteristics include intensity, quality, distribution and temporal relationships. The principles of tumour-directed pain control include modifying the source of pain by treating the cancer and the inflammatory response to cancer, altering the central perception of pain and interfering with nociceptive transmission within the central nervous system.