Cancer pain deserves its own category because it is unique in cause and in therapies. Cancer pain consists of both acute pain and chronic pain from the neoplasm itself and from the therapies associated with it, such as surgery, chemotherapy, radiation, and immunotherapy. In addition, patients with cancer pain may also have acute or chronic non–cancer-related pain, and this possibility should not be overlooked when taking care of cancer patients.
Cancer pain includes somatic pain (eg, neoplastic invasion of tissue such as painful fungating chest wall masses in breast cancer), visceral pain (eg, painful hepatomegaly from liver metastases, stretching the liver capsule), neuropathic pain (eg, neoplastic invasion of sacral nerve roots), or pain from a paraneoplastic syndrome (eg, peripheral neuropathy related to anti-Hu antibody production). Chemotherapy can cause peripheral neuropathies, radiation can cause neuritis or skin allodynia, and surgery can cause persistent postsurgical pain syndromes such as post-mastectomy or post-thoracotomy pain syndromes.
Generally, patients with cancer pain do not exhibit a single type of pain—they may have multiple reasons for pain and thus benefit from a comprehensive and multimodal strategy. The WHO Analgesic Ladder, first published in 1986, suggests starting medication treatment with nonopioid analgesics, then weak opioid agonists, followed by strong opioid agonists. It should be noted that this ladder was developed to promote pain management in areas of the world where no pain management has been offered. While opioid therapy can be helpful for a majority of patients living with cancer pain, therapy must be individualized depending on the individual patient, their family, and the clinician. For example, if one of the goals of care is to have a lucid and coherent patient, opioids may not be the optimal choice; interventional therapies such as implantable devices may be an option, weighing their risks and costs against their potential benefits. Alternatively, in dying patients, provided there is careful documentation of continued, renewed, or accelerating pain, use of opioid doses exceeding those recommended as standard for acute (postoperative) pain is acceptable.
One of the unique challenges in treating cancer pain is that it is often a “moving target,” with disease progression and improvements in disease progression or worsening pain directly stemming from chemotherapy, radiation, or immunotherapy. Therefore, frequent adjustments may be required to any pharmacologic regimen. Interventional approaches such as celiac plexus neurolysis and intrathecal therapy are well-studied and may be appropriate both for analgesia as well as reduction of side effects from systemic medications. Radiation therapy (including single-fraction external beam treatments) or radionuclide therapy (eg, strontium-89), which aims to decrease the size of both primary and metastatic disease, is one of the unique options for patients with pain from cancer.
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