Pain is the result of a physiological series of electrical and chemical events that occur in the body. The International Association for the Study of Pain defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.”

Pain receptors are bare nerve endings that are widely distributed throughout the body in the skin and mucous membranes. When pain receptors are triggered by mechanical, chemical, or thermal stimuli, the pain signal is transmitted through the nerves to the spinal cord and then to the brain.

Pain depends on many factors such as the type of cancer the stage of the disease, and the patient’s tolerance.

Cancer pain can result from the following:

• Blocked blood vessels causing poor circulation
• Bone fracture from metastasis
• Infection
• Inflammation
• Psychological or emotional problems
• Side effects from cancer treatments such as chemotherapy and radiation
• Tumor exerting pressure on a nerve

Initially, pain may produce physiological signs such as grimacing, rapid heart rate, sweating, and rapid breathing. Patients with pain lasting more than 3 months (chronic pain) often do not display physiological signs and as a result, chronic pain often is undertreated. Communication between the patient and physician is important to ensure adequate pain relief.

When possible, if cancer pain is caused by a tumor, removing or reducing the tumor that is causing it may help. When the tumor cannot be removed, the pain can be treated in other ways.

Incidence and prevalence of cancer pain

Studies have shown that 90% of patients with advanced cancer experience severe pain and pain occurs in 30% of all cancer patients, regardless of the stage of the disease. As many as 50% of patients may be undertreated for cancer pain, yet not all cancer patients experience pain. Pain usually increases as cancer progresses.

The most common cancer pain is from tumors that metastasize to the bone. Sixty to eighty percent of cancer patients with bone metastasis experience pain. The second most common cancer pain is caused by tumors infiltrating the nerve. Tumors near neural structures may cause the most severe pain. The third most common pain associated with cancer occurs as a result ofchemotherapy, radiation, or surgery.

Cancer pain may occur in different parts of the body. In one study, more than 80% of patients experienced pain in two distinct areas, and more than 30% experienced pain in three or more distinct areas.

Chronic cancer pain

Effectively treating chronic pain poses a great challenge for physicians. Pain from cancer often affects a person’s life in many ways. It can change someone’s personality, ability to function, and quality of life.

According to the American Cancer Society, chronic cancer pain may involve persistent pain and breakthrough pain. Persistent pain is continuous and may last all day. Breakthrough pain is a brief flare-up of severe pain that occurs even while the patient is regularly taking pain medication. It usually comes on quickly and may last from a few minutes to an hour. Many patients experience a number of episodes of breakthrough pain each day.

Breakthrough cancer pain can result from the cancer or cancer treatment, or it may occur during a certain activity (e.g., walking, dressing, coughing). It also can occur unexpectedly, without a preceding incident or clear cause. Breakthrough pain usually is treated with strong, short-acting pain medications that work faster than persistent pain medications.

Regardless of the type of pain you may be experiencing due to cancer, it is important to discuss it with your specialists and be persistent.  If you feel like your physicians aren’t taking your pain seriously enough, you may need to elicit help from family members and schedule a conference with your primary caregiver and your doctors to convey your level of pain.  Remember that it is not okay to suffer in silence.  Ask for help when you need it.  You will feel better and your family will rest easier knowing that their loved one is getting some relief from their pain.

Jennifer Kelly is a molecular geneticist and oncologist.

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