Bone pain in patients with cancer is commonly caused by cancer cells that have spread to the bones, called bone metastases. Bone pain is commonly the first symptom of bone metastases and may lead to tests that will confirm the diagnosis. Treatment for bone pain is intended to relieve the pain, treat fractures, reduce the risk of fracture, and prevent or delay additional bone complications. Treatment options include pain medications, bisphosphonate drugs, radiation therapy, and/or surgery.
A common cause of bone pain is metastatic cancer. The spread of cancer from its site of origin to another location in the body is called metastasis. A bone metastases is not a new cancer, but consists of cancer cells from the original cancer, such as breast, prostate, lung, kidney, or thyroid, that have spread to bone.
Cancer cells can spread, or metastasize, through the blood and lymph systems. Bone is one of the most common locations in the body to which cancer metastasizes. Bone metastasis usually occurs by way of the bloodstream. A cancer cell may break away from the original location in the body and travel in the circulatory system until it gets lodged in a small capillary network in bone tissue. Cancer may also spread to bone by erosion from the adjacent cancer, though this occurs less frequently than spread by the bloodstream.
The pain occurs with bone cancer because the cancer disrupts the balance of normal cellular activity in the bones, causing damage to the bone tissue. Normal bone is constantly being remodeled, or broken down and rebuilt. Cancer cells that have spread to the bone disrupt this balance between the activity of osteoclasts (cells that break down bone) and osteoblasts (cells that build bone), resulting in either weakened or excessively built-up bone. This damage can either stretch the periosteum (thick membrane that covers bone) or stimulate nerves within the bone, causing pain.
Bone metastases are usually diagnosed because the patient experiences pain near the metastases and reports this to their doctor. The doctor may then complete an x-ray or a more complicated procedure called a bone scan to confirm that the pain is caused by cancer-related damage to the bones. In a bone scan, low level radioactive particles are injected into a vein. They circulate through the body and some are absorbed into the bones. A high concentration of these radioactive particles on the bone scan results indicates the presence of rapidly growing cancer cells in the bone.
Bone pain may be hard to differentiate from ordinary low back pain or arthritis. Usually the pain due to bone metastasis is fairly constant, even at night. It can be worse in different positions, such as standing, which may compress the cancer in a weight bearing bone. If pain lasts for more than a week or two, doesn't seem to be going away, and is unlike other pain that may have been experienced, it should be evaluated by a physician.
Bone metastases generally occur in the central parts of the skeleton, although they may be found anywhere in the skeletal system. Common sites for bone metastases are the back, pelvis, upper leg, ribs, upper arm, and skull. More than 90% of all metastases are found in these locations.
The goal of treatment for bone pain caused by bone metastases is to relieve the pain, treat fractures, reduce the risk of fracture, and prevent or delay additional bone complications. Treatment options for bone metastases include pain medications, bisphosphonate drugs, radiation therapy, and/or surgery.
Pain medications: Cancer-related bone pain can be managed with various pain medications. Despite the claim that 90% of adult cancer patients' pain can be relieved, uncontrolled cancer-related pain is still a concern, particularly for patients who are living at home. Research presented at the 2003 Annual Meeting of the Oncology Nursing Society indicates that most cancer patients are not prescribed enough medication to control their pain.1
The World Health Organization recommendations for relief of cancer pain indicate that the severity of a patient's pain, rated on a scale of 1-10, will dictate what type of pain medication is used.2
Pain medications may have side effects, including sleepiness, constipation, dizziness, nausea, and vomiting. Relief from pain medications is temporary and the pain may return in a short time; thus, medications are best used at the onset of pain or at regular intervals.
Bisphosphonate drugs can effectively prevent loss of bone that occurs from metastatic lesions, reduce the risk of fractures, and decrease pain. Bisphosphonate drugs work by inhibiting bone resorption, or breakdown. Bone is constantly being “remodeled” by two types of cells: osteoclasts, which break down bone; and osteoblasts, which rebuild bone. Although the exact process by which bisphosphonates work is not completely understood, it is thought that bisphosphonates inhibit osteoclasts and induce apoptosis (cell death) in these cells, thereby reducing bone loss. There is also evidence that these drugs bind to bone, thereby blocking osteoclasts from breaking down bone.
Cancer cells release various factors that stimulate osteoclastic activity, causing increased breakdown of bone. By inhibiting osteoclasts, bisphosphonate drugs effectively reduce the detrimental impact that cancer cells have on bone density. An analysis of the results from 30 clinical trials demonstrates that patients with bone metastases treated with a bisphosphonate had a delayed time to skeletal fractures, a reduced need for radiation therapy to treat bone metastasis, a reduction in hypercalcemia (high blood levels of calcium), and a reduction in the need for orthopedic surgery.3
Bisphosphonate drugs that are FDA-approved for the treatment of cancer-related skeletal complications include Zometa® (zoledronic acid) and Aredia® (pamidronate). Of these two drugs, Zometa® appears to demonstrate the strongest activity. An added benefit of Zometa® is that it is administered in a dose ten times lower than Aredia®, which considerably reduces the administration time from several hours to 15 minutes, resulting in a more convenient regimen for patients.
Bisphosphonates have been shown to prevent or delay bone destruction and related pain in clinical trials involving patients with bone metastases related to:
Radiation therapy: For metastatic lesions that do not represent an immediate risk of fracture, radiation is effective for reducing bone pain and progression of the cancer. Radiation is especially useful when metastatic lesions are limited to a single area.
One type of radiation therapy is called radiopharmaceutical therapy. This approach involves the injection of a radioactive substance, such as strontium-89, into a vein. This substance is attracted to areas of bone that contain cancer. Providing radiation directly to the bone in this way destroys active cancer cells in the bone and can relieve symptoms. Two possible side effects of radiopharmaceutical therapy are decreased blood counts with increased risk of bleeding, and rarely, leukemia.
Surgery: When there is an immediate or significant risk of fracture, surgery may be necessary to stabilize the weakened bone. Metal rods, plates, screws, wires, nails, or pins may be surgically inserted to strengthen or provide structure to the bone damaged by metastasis.
1 Oncology Nursing Society. ONS Position Paper on Pain. Pittsburgh PA ; 2002.
2 Chen H, Wilkie D, Huang H. Opiod Prescritption for Cancer Pain Management. Proceedings form the 2003 Annual Meeting of the Oncology Nursing Society. Abstract #147.
3 Ross JR, Saunders Y, Edmonds PM, et al. Systematic Review of Role of Bisphosphonates on Skeletal Morbidity in Metastatic Cancer. British Medical Journal 2003; 327:469-471.