Pain has been defined as “An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” by the International Association for the Study of Pain (IASP Pain Terminology, 1994). It is a subjective experience while it is also a complex perception produced by the brain and the nervous system which basically signals the occurrence of actual or potential tissue damage. The term “nociception” is generally used to refer to the perception of pain. Pain has physical as well as emotional consequences, and, at its worst, the potential to curtail productivity, and the sense of well-being. The presence of uncontrolled pain in cancer patients can often serve as a constant reminder of their dreaded disease that induces them to brood over their anticipated death.
About 25% to 30% of patients with recently diagnosed and metastatic cancers are affected by pain (Cleeland et al., 1994) whereas in advanced stages of cancer the number could be as high as 80% (Abrahm, 1998. Wootton, 2004. McNicol et al., 2004. Mercadante and Fulfaro, 2005). A vast majority (90%) of patients with metastasis to osseous structures report pain (Haegerstam, 2001). The causes of cancer pain could be due to cancer itself or its treatment, or other causes. The presence of tumour could result in neuropathic pain due to direct compression of nerves or plexus or spinal cord. Neuropathic pain can also be caused by chemotherapy with drugs such as vinca alkaloids or radiation therapy (Pharo and Zhou, 2005). It becomes imperative, therefore, to understand the various forms and mechanisms of pain in order to adopt the most appropriate strategy for pain management. A treatment plan that is easy to administer, provides the greatest pain relief with few (or none) side effects is what is desirable.