Most patients, if they do not have pain at the diagnosis of cancer, experience pain from cancer as the disease progresses. Because there may be new pain or progressively increasing pain, frequent re-evaluation is necessary to optimize therapy. Pain related to cancer may arise from nerves or from any tissues or organs in the body, causing various pain syndromes.
Causes of cancer pain
About 70% of all cancer pain is related to cancer that has metastasized to the bone. Another 15% of all cancer pain is caused by complications from anticancer therapy, and the remaining 15% is due to unrelated conditons.
Bone pain due to metastasis
Metastasis is the spread of cancer from one part of the body to another. Tumor cells detach from the original (primary) tumor, travel in the bloodstream, and are deposited in distant tissue, where they grow.
The primary tumors that have the greatest tendency to metastasize to the bone are breast, prostate, lung, kidney, and thyroid tumors. The presence of metastasis to bone invariably results in pain, and is confirmed by X-ray, bone scans, CT scans, or MRI scans.
The pain does not generally correlate with the extent or size of the metastasis, but is related to the type of primary cancer that is present, and its effect on normal bone activity at the new site. Bone metastases indicate progressive disease. The rate of progression, however varies significantly depending on the type of primary cancer and other factors such as immune status and nutritional status.
The complications of metastasis to the bones have an important impact on the patient's quality of life. For example, tumor cells in bone may cause localized "thinning" of the bone, similar to what occurs in osteoporosis. These destructive bone lesions cause ongoing pain, reduction in mobility, neurological defects, and bone fractures.
Hypercalcemia (high calcium levels in the body) is another frequent complication of certain types of bony metastases. These high calcium levels are due to the breakdown of bone, or to hormonal effects on calcium metabolism. Hypercalcemia may cause nausea, vomiting, constipation, loss of appetite, weakness, dehydration, and confusion. Because these are all frequent symptoms that can be caused by many other conditions in cancer patients, hypercalcemia is often overlooked as the cause.