Introduction

Pain is the most feared symptom of cancer, and its management is one of the prime duties of the physician. Between 30% and 50% of cancer patients undergoing active treatment for a solid tumor will experience chronic pain, and this frequency can rise to 90% in advanced cases. Although 'adequate pain relief' using simple drug treatment has been claimed for 90% of patients with cancer pain, this rate is no often achieved in practice. The first step in managing the problem is proper evaluation, and the authors of the review summarized here have outlined the principles involved.

Assessment of cancer pain

Pain is the perception of tissue injury (nociceptive pain) or aberrant nerve stimulation (neuropathic pain), colored by affective and cognitive reactions (psychogenic pain). Thus, as it is mostly subjective, patient self-reports represent the gold standard for its assessment. A full history, examination, and appropriate lab and imaging studies should reveal the relationship between the disease process and the origin of the pain. But the time-course, intensity, quality, and exacerbating or relieving factors are paramount in determining the best management strategy.

Acute pain syndromes

These are commonly caused by a diagnostic or therapeutic intervention: lumbar puncture, marrow biopsy, pleural tap, chemotherapy (especially parenteral), hormone therapy (e.g. gynecomastia), immunotherapy (arthralgia, myalgia), and radiation (mucositis, proctitis). Sometimes acute pain breakthroughs occur in patients with well-controlled chronic pain.

Chronic pain syndromes

There are a number of chronic tumor-related nociceptive pain syndromes, the most common being due to bone pain. It is not known why some bone metastases are painless, and others are painful. When the spine is involved, there is the potential for damage to the spinal cord or nerve roots, with distressing consequences. Early diagnosis and treatment of the tumor can prevent neurological deficits.

Chronic neuropathic pain syndromes can be caused by tumor infiltration or neural compression; they are highly variable in location and type of pain, and may be associated with motor, sensory, or autonomic dysfunction.

Treatment-related nociceptive chronic pain, related to chemotherapy, radiation, or surgery, is relatively uncommon. Radiation or steroid therapy may produce osteonecrosis, and intraperitoneal chemotherapy or radiation can produce chronic abdominal pain; it's important to be able to distinguish such syndromes from tumor recurrence.

Most treatment-related pain syndromes are neuropathic; examples are the post-mastectomy syndrome (a tight, burning sensation in the upper arm and axilla, due to intercostobrachial nerve injury), and post-radiation fibrosis involving peripheral nerve (ocurring months after therapy, progressive, and associated with motor weakness, skin changes, and lymphedema).

Persistent polyneuropathy is sometimes reported in association with neurotoxic chemotherapy (e.g. vincristine, cysplatin); it often improves when the treatment is discontinued.

Associated dimensions

Suffering by cancer patients is not limited to the perception of pain. Additional dimensions - e.g. fatigue, psychological misery, and social distress - must also be addressed, or at least not exacerbated, by pain treatment. Full assessment requires a continuous, open dialog between patient and physician. Incorporation of a team of professionals will help cover all aspects of the quality of life of the patient, not just physical and psychological well-being, but also household, social, spiritual, and financial factors. Hospice programs are particularly suitable in this regard.

When all aspects of a patient's suffering are taken into consideration, the expression 'palliative care' can be applied to management. As the end of life approaches, palliative care must intensify, and ensure that the patient's comfort has absolute priority. The part of palliative care concerned with pain management is considered in a companion article to this one (see link below).