Understanding cancer pain.

The pathogenesis of cancer pain, the incidence of pain associated with specific types of malignant tumors, and the nature of acute and chronic pain are discussed, and alternative delivery systems for pain management are described. More than 80% of cancer patients with advanced metastatic disease suffer moderate to severe pain. Most cancer pain is caused by direct tumor infiltration; approximately 20% of cancer pain may be attributed to the effects of surgery, radio-therapy, or chemotherapy. The incidence of cancer pain is related to tumor type; 70% or more of patients with tumors of the bone, cervix, and ovaries suffer cancer-related pain, while only 5% of patients with leukemia have pain. Pain is defined by the organs involved. Somatic pain is usually dull and well localized; visceral pain is generalized and difficult to describe. Other types of pain, including deafferentation pain and referred pain, are particularly difficult to manage. Cancer pain may be acute or chronic. The latter may cause psychological reactions that make effective treatment more challenging. Opiate analgesic agents, administered by the epidural or intrathecal routes, block pain more selectively and produce fewer adverse reactions than systemic analgesic agents. The duration and onset of analgesia depend on the lipophilicity of the agent used. Because pain is the most common complaint of the patient with cancer, clinicians should be aware of the range of pharmacologic and nonpharmacologic analgesic modalities available to them. Familiarity with newer modalities and delivery routes, such as spinal administration of opiate analgesics, is recommended.