Of all the symptoms faced by patients with advanced cancer, pain is perhaps the best understood, and research in this area has a higher level of support than the study of other symptoms (see previous section). Several issues related to the subjective measurement of pain have been successfully addressed, and pain-related patient outcome variables can be specified for clinical, health services research, and epidemiologic studies. It is estimated that a majority of cancer patients could have their pain controlled, at least until the last week or two of life.
Current treatment of cancer pain is beginning to be codified into evidence-based and practice-based guidelines (practice based refers to guidelines that blend expert opinion and research evidence, where the evidence alone is not sufficient), which suggests a maturity of knowledge that does not exist for other symptoms. The common syndromes that account for the majority of cancer pain are well described and dictate specific treatment approaches. In contrast to other areas of research under discussion, there is a group of well-trained investigators who are able to conduct both basic and clinical research in the area. As described above, the biggest problems—which are amenable to health services research—are in getting physicians and patients to use pain medications to their best advantage. However, there are still major basic and clinical research issues to be dealt with, and research in cancer pain is also as affected by compartmentalization and lack of organizational support, funding, and structure as is research in other areas of end-of-life care. One approach to alleviating this problem is to facilitate networking among cancer pain investigators and basic scientists who are working in separate disciplines.
Basic research into the mechanisms of cancer pain has been limited by two major gaps in knowledge: (1) a poor understanding of the specific nature of cancer pain and (2) the lack of appropriate animal models.
Cancer pain potentially involves somatic, visceral, and neuropathic components. There have been marked advancements in understanding the mechanisms of cutaneous somatic pain over the past 20 years. These were largely first driven by the landmark studies of Lewis, and later Hardy and colleagues, that described the phenomena of primary and secondary hyperalgesia. The neurochemical basis of pain is becoming better understood; however, clinical applications of these findings have not yet had an impact on treatment.
Neuropathic pain, produced by nerve destruction and prominent in both cancer and AIDS, is poorly understood and difficult to treat (Woolf