Bone Basics

Bone is a type of connective tissue made up of minerals, such as calcium and phosphate, and the protein collagen. The outer layer of bone is called the cortex and the spongy center of bone is called cancellous bone. The bone marrow fills in the spaces within the spongy bone. Bone tissue is porous and alive, with blood vessels running through it.

Bone constantly repairs and renews itself through a process called remodeling. Two kinds of cells are involved:

Bones carry out a number of functions in the body.

• The skeleton provides structural support for the body.
• Bones store and release minerals that the body needs to function, such as calcium, magnesium, phosphorus and sodium when the body needs them.
• Bone marrow produces and stores blood cells--red blood cells that transport oxygen from the lungs to the rest of the body; white blood cells that fight infections; and platelets that help the blood clot.
• When cancer cells invade the bone, any of these functions may be affected.

Spreading

When cells break away from a cancerous tumor (a primary tumor) they can travel to other parts of the body through the bloodstream or the lymph vessels. Moving through the bloodstream or lymphatic system, cancer cells can lodge in an organ at a distant location and establish a new (secondary) tumor. Bone is the most common site of breast cancer recurrence.

Secondary tumors that have spread to bone (bone mets) through the process known as bone metastasis are not the same as primary bone cancer that starts in the bone (sarcoma). A tumor that has metastasized to bone is made up of abnormal cancer cells from the original tumor site and not of bone cells. Breast cancer that spreads to the bone consists of breast cancer cells. In this case, bone metastasis would be called metastatic breast cancer.

Symptoms of Bone Metastases

Bone metastases can cause these symptoms.

• Bone pain. Pain is the most common symptom of bone metastasis. It’s usually the first symptom that people notice. At first, the pain may come and go. It tends to be worse at night or with bed rest. Eventually, the pain may increase and become severe. Not all pain indicates metastasis. The doctor can help distinguish between pain from metastasis and aches and pains from other sources.
• Broken bones. Bone metastasis can weaken bones, putting them at risk for breaking. In some cases, a fracture is the first sign of bone metastasis. The long bones of the arms and legs and the bones of the spine are the most common sites of fracture. A sudden pain in the middle of the back may indicate a cancerous bone breaking and collapsing.
• Numbness or weakness in the legs, trouble urinating or having a bowel movement, or numbness in the abdomen. These are all signs that the spinal cord may be compressed. When cancer metastasizes to the spine, it can squeeze the spinal cord. The pressure on the spinal cord may cause these symptoms, as well as back pain. These symptoms should be told to a doctor or nurse right away. If untreated, they can cause paralysis.
• Loss of appetite, nausea, thirst, constipation, tiredness, or confusion. These are all signs that there are high levels of calcium in the blood. Bone metastases can cause calcium to be released from the bones and into the bloodstream. This condition is called hypercalcemia. These symptoms should be told to a doctor or nurse right away. If untreated, they may cause a coma.
• Other symptoms. If bone metastasis affects the bone marrow, people may have other symptoms related to decreased blood cell counts. For instance, red blood cell levels may drop, causing anemia. Signs of anemia are tiredness, weakness, and shortness of breath. If white blood cells are affected, people may develop infections. Signs of infection include fevers, chills, fatigue, or pain. If the number of platelets drops, bruising or abnormal bleeding may occur.

It is important for people to discuss any of these symptoms with their doctor. Detecting and treating this condition early can help reduce complications.

Diagnosis

When a patient experiences symptoms suggestive of bone metastasis, various tests can be done to confirm the cause. In some cases bone metastasis may be detected before symptoms arise.

X-rays. Radiographic examination, or X-rays, can provide information about what part of the skeleton the cancer has spread to as well as the general size and shape of the tumor or tumors. (It is common for more than one metastasis to be found.)

Bone scan. Bone scans can detect bone metastasis earlier than X-rays can. They also allow the doctor to monitor the health of all the bones in the body, including how they are responding to treatment.

In a bone scan, the patient is given an injection of a low amount of radioactivematerial (much lower than that used in radiation therapy). The radioactive substance is attracted to diseased bone cells throughout the body. Diseased bone appears on the bone scan image as darker, dense areas. Conditions other than metastasis, such as arthritis, infections, or previous fractures that have healed, may also be picked up on a bone scan, although the patterns they produce are often different from those produced by cancer. Additional tests can help distinguish among these other conditions.

Computed Tomography (CT) scan. The CT scan provides X-ray images to look at cross sections of organs and bones in the body. Rather than provide one image as a conventional X-ray does, the CT scanner takes many pictures as it rotates around the body. A computer combines the images into one picture to show if cancer has spread to the bones. It is particularly helpful in showing osteolytic metastases that may be missed with the bone scan. Magnetic Resonance Imaging (MRI). MRI scans use radio waves and strong magnets instead of X-rays to provide pictures of bones and tissues. They are particularly useful in looking at the spine.

Laboratory tests. Bone metastasis can cause a number of substances, such as calcium and an enzyme called alkaline phosphatase, to be released into the blood in amounts that are higher than normal. Blood tests for these substances can help diagnose bone metastasis. Doctors also can measure the levels of these chemicals over time to monitor a patient's response to treatment. Elevated levels of these substances can indicate other medical conditions besides metastasis.

Treatment

Most doctors believe the most important treatment for bone metastases is treatment directed against the cancer. This is usually done with systemic therapies. Systemic therapies enter the bloodstream and can reach cancer cells that have spread throughout the body. Systemic therapies include chemotherapy or hormone therapies that are taken by mouth or injected. There are also drugs called bisphosphonates that can help make diseased bones stronger and help prevent fractures. Bisphosphonates are used along with the chemotherapy or hormone therapy for bone metastasis. These treatments are discussed in more detail below. Another form of systemic treatment is a type of drug called a radiopharmaceutical. This type of drug may be used to deliver radiation to many bones at once. If systemic treatments work, the symptoms of the bone metastases will go away and new symptoms are not likely to develop soon. Bone problems may also be treated by doing something to the bone that has cancer in it. This is often done using local treatments, which are directed at a single area. Local treatments such as radiation therapy can relieve the pain in a bone by destroying the cancer. Sometimes a bone might look as if it is close to breaking. To prevent this, your doctor may recommend surgery that involves reinforcing the bone by placing a thin steel rod or other kind of metal support in it. Sometimes, the doctor will inject glue to make the bone more stable. It is much easier to keep a damaged bone from breaking than to try and repair it after it has broken.

Pain Management Therapy

Pain usually results when a tumor pushes on bones, nerves, or other organs in the body. Many different drugs or drug combinations can be used to treat bone metastasis pain. Sometimes medications are used along with surgery, radiation, or other treatments to provide relief. The side effects of the different drugs and drug combinations can vary. Some patients experience mild side effects while others have a more intense reaction. Your doctor will discuss with you the medication(s) that he/she feels will work best for you and the possible side effects.

Radiation Therapy

Radiation therapy, often called radiotherapy, involves the use of ionizing radiation. Ionizing radiation refers to the high-energy rays that are given off during treatment. The radiologist directs these rays to injure or destroy cancer cells in the area of the bone metastasis or tumor. Although some normal (noncancer) cells are destroyed in the process, these cells can repair themselves and restore normal function. The goal of radiotherapy is to destroy cancer cells so that they cannot reproduce and grow. Patients also benefit from radiotherapy because it reduces bone pain and lessens the chance of fractures. Again, patients should discuss possible side effects of therapy with their doctor.

Surgical Therapy

In most cases, surgery can restore the function of the original bone. The type of surgery will depend upon the location and size of the bone metastasis tumor. Surgery usually involves removing all or part of the tumor and stabilizing the bone to prevent breakage. With fractures or impending fractures, surgery could include placement of metal plates, rods, screws, wires, nails, and/or pins, or prostheses. The purpose of these tools is to strengthen or provide structure to the bone. The surgeon hopes that doing this will help the functional recovery of patients. Another option for surgery includes reconstruction of bones or joints. Reconstruction is a procedure where metal, plastic, allografts or a combination of these replaces the damaged bone in the area of the metastasis. Over time, this piece becomes part of the human skeleton.

Some patients may experience pain or be limited in their physical activity for a period of time after surgery. Therefore, it is important to be aware of the recovery time needed for the different surgical procedures. Although there are many surgical options that are available for bone metastasis patients, most patients do not need surgery. Your doctor can discuss the options that would be best for you.

Radiopharmaceutical Therapy

The purpose of radiopharmaceutical therapy is to deliver radiation to tumor cells without harming normal cells. This type of therapy involves the injection of active metals that give off radiation particles in the patient. Currently, these include the metals Samarium and Strontium. By providing radiation directly to the bone, these metals target and destroy the active cancer cells in the bone. Pain is also decreased or relieved entirely. This therapy has been shown to decrease platelet and white blood cell production in some patients as they undergo more treatments. However, most patients like radiopharmaceutical therapy because they experience very few side effects once treatment is completed.

Medical Therapy

Bisphosphonates are a class of medications shown to be effective in treating bone metastases in both breast cancer and myeloma patients. The kind of bisphosphonates given for bone metastases is usually given through an IV line (intravenously). Specifically, they decrease the risk of fractures and decrease pain from bone metastasis. They also reduce the number of future radiation treatments for these patients. Commonly, patients take bisphosphonates along with other forms of treatment.

Chemotherapy can be given at the same time as bisphosphonate therapy but they are not the same. If you are receiving bisphosphonates, your doctor will monitor your blood tests and ask you about the side effects you have experienced with treatment. You and your doctor will decide which treatment is best after considering a number of factors: site, size and extent of the bone metastasis, cancer stage, and the types of treatment you’ve had in the past. Your age, overall health, and symptoms will also play a part in the choice of treatments. Since each patient’s case may be a little different, it is best that you work with your doctor to decide the best option for you. Also, remember that each patient may have a different reaction to these treatments. Some people have very few side effects while other people have many. Your doctor can help you learn what to expect.