Cancer pain is usually caused directly by neoplastic injury to pain-sensitive structures. For this reason, primary antineoplastic therapy, including radiation, chemotherapy, and palliative surgery, should be considered part of an analgesic strategy in some cases. When therapy directed at the tumor is inappropriate, is not feasible, is ineffective, or causes painful therapy-related syndromes, symptomatic analgesic therapies become the overriding concern. Opioid-based pharmacotherapy is the mainstay approach, but adjunctive anesthetic, surgical, psychiatric, and physical modalities may be essential as well (see Chapter 54, Cancer Pain Syndromes). Pharmacologic approaches may be systemic or regional (anesthetic).
The World Health Organization (WHO) proposed a three-step approach—the analgesic ladder—to the selection of drugs for the treatment of cancer pain (Fig. 55-1).1 Step 1, for mild pain, uses nonopioid analgesics and adjuvant drugs. Adjuvant drugs can be either nontraditional analgesics or drugs added to manage the side effects of the primary analgesics. For more intense pain, an opioid is added. Some opioids are used conventionally for moderate pain, and others are used for severe pain. This approach is designed to be simple to understand and usable around the world. Uncontrolled field testing has found the WHO guidelines effective for 70% to 100% of patients with cancer.2 The aim of this chapter is to provide an overview of the approach to medical management of cancer pain, particularly covering the use of systemic analgesics recommended by the WHO's analgesic ladder for cancer pain.
The three-step analgesic ladder for cancer pain treatment. (Reproduced by permission of World Health Organization. Cancer Pain Relief, 2nd ed. Geneva: Author; 1996.)
Pain is often underrecognized in cancer patients. Cleeland et al.3 surveyed outpatients with metastatic cancer and physicians from 54 treatment centers. They found that 42% of 597 patients with pain were not receiving adequate analgesia by the WHO guidelines (see Fig. 55-1). Insufficient pain relief was particularly common among minorities, women, and elderly adults. An important barrier to effective pain management was a discrepancy between the patient's and the physician's assessment of the extent to which pain was interfering with daily activities. The data underscore the importance of accurate pain assessment in providing adequate cancer pain relief.
The assessment should allow inferences about the pain mechanisms, identification of the pain syndrome (see Chapter 44, Cancer Pain Syndromes), and classification of the relationship between the pain and the disease. The clinician must also assess the functional impact of the pain and psychosocial comorbidities. It is essential to accept the patient's report of pain at face value. Pain should be assessed frequently and systematically, especially when a new pain is reported or a new analgesic treatment is initiated. The location, intensity, and quality of the pain; aggravating and relieving factors; pain impact or interference with ...