BONE METASTASES DEFINITION
Bone metastasis occurs when cancer cells spread from their original site to a bone.
Nearly all types of cancer can spread (metastasize) to the bones. But some types of cancer are particularly likely to spread to bone, including breast cancer and prostate cancer.
Bone metastasis can occur in any bone but more commonly occurs in the spine, pelvis and thigh. Bone metastasis may be the first sign that you have cancer, or bone metastasis may occur years after cancer treatment.
Bone metastasis can cause pain and broken bones. With rare exceptions, cancer that has spread to the bones can’t be cured. Treatments can help reduce pain and other symptoms of bone metastases.
BONE METASTASES CAUSES
Bones provide fertile ground for the growth of tumor cells, because they are areas of constant cell turnover and growth. And bone cells release substances that may prompt faster cancer growth. Cancer cells may also attach better to bone than to other substances in the body for some reason.
Cancer cells can go anywhere, but they often go to the bones with the greatest blood supply. This includes bones in the:
- Upper arms
BONE METASTASES PATHOPHYSIOLOGY
Previously, the 2 main theories of how tumor cells metastasize and grow in bones were Paget’s fertile soil hypothesis and Ewing’s circulation theory. However, a substantial amount of work has more clearly defined the metastatic process to bone. Bone metastases occur in a predictable distribution. In order of frequency, the most common locations include the following:
- Proximal limb girdles
The red marrow theory, combined with knowledge about the cytokine stimulation of metastases, provides an excellent explanation of how this distribution occurs.
Metastases distal to the knee and elbow are extremely uncommon, but approximately 50% of these acral metastases are secondary to primary lung tumors. Carcinomas, such as those of the breast and prostate, rarely exhibit such a distinct pattern.
BONE METASTASES SYMPTOMS
Sometimes, bone metastasis causes no signs and symptoms.
When it does occur, signs and symptoms of bone metastasis include:
- Bone pain
- Broken bones
- Urinary incontinence
- Bowel incontinence
- Weakness in the legs or arms
- High levels of calcium in the blood (hypercalcemia), which can cause nausea, vomiting, constipation and confusion
BONE METASTASES DIAGNOSIS
In some cases, your doctor may find bone metastasis before you have symptoms. In some cancers, where bone metastasis is common, your doctor may order tests to make sure the cancer has not spread to the bones, before recommending treatment. When you have symptoms of bone metastasis, doctors can do the following tests to find the cause:
- Bone scan
- Computed tomography scan
- Lab tests
- Magnetic resonance imaging scan
BONE METASTASES TREATMENT
Treatments for bone metastasis include medications, radiation therapy and surgery. What treatments are best for you will depend on the specifics of your situation.
Medications used in people with bone metastasis include:
- Bone-building medications. Medications commonly used to treat people with thinning bones (osteoporosis) may also help people with bone metastasis. These medications can strengthen bones and reduce the pain caused by bone metastasis, reducing the need for strong pain medications. Bone-building medications may also reduce your risk of developing new bone metastasis.
These drugs can be administered every few weeks through a vein in your arm or through an injection. Oral forms of these medications are available, but they generally aren’t as effective as the IV forms, and may cause digestive tract side effects.
Bone-building medications can cause temporary bone pain and kidney problems. They increase your risk of a rare but serious deterioration of your jawbone (osteonecrosis).
- Chemotherapy. If cancer has spread to multiple bones, your doctor may recommend chemotherapy. Chemotherapy travels throughout your body to fight cancer cells. Chemotherapy can be taken as a pill, administered through a vein or both. Side effects depend on the specific chemotherapy drugs you’re given. For cancers that are sensitive to chemotherapy, chemotherapy may be the best way to alleviate pain from bone metastases.
- Hormone therapy. For cancers that are sensitive to hormones in the body, treatment to suppress those hormones may be an option. Breast cancers and prostate cancers are often sensitive to hormone-blocking treatments.
Hormone therapy can involve taking medications to lower natural hormone levels or medications that block the interaction between hormones and cancer cells. Another option is surgery to remove hormone-producing organs — in women, the ovaries, and in men, the testes.
- Pain medications. Pain medications may control the pain caused by bone metastasis. Pain medications may include over-the-counter pain relievers, such as ibuprofen (Advil, Motrin IB, others), or stronger prescription pain relievers, such as morphine (Avinza, MS Contin, others).
It may take time to determine what combination of pain medications works best for you. If you’re taking medications but still experiencing pain, tell your doctor. A pain specialist may be able to offer additional pain-relieving options.
- Steroids. Medications known as steroids can often help to relieve pain associated with bone metastases by decreasing swelling and inflammation around the sites of cancer. These steroids are different from the types of steroids that bodybuilders or athletes use to build muscle.
These can work quite quickly to help pain and prevent some cancer complications, but they also must be used very cautiously because they have side effects, especially when used for prolonged periods.
- Targeted therapy. For many cancers, a new class of medications known as targeted therapies is available. These medications attack specific abnormalities within the cancer cells.
Certain cancers may respond very well to these treatments. For example, breast cancer cells that are HER2 positive can respond to trastuzumab (Herceptin) therapy.
External radiation therapy
Radiation therapy uses high-powered energy beams, such as X-rays, to kill cancer cells. Radiation therapy may be an option if your bone metastasis is causing pain that isn’t controlled with pain medications or if the pain is confined to a small number of areas.
Depending on your situation, radiation to the bone can be administered in one large dose or several smaller doses over many days. Side effects of radiation depend on the site being treated and its size.
Surgical procedures can help stabilize a bone that is at risk of breaking or repair a broken bone.
- Surgery to stabilize the bone. If the bone is in danger of breaking due to bone metastasis, surgeons can stabilize the bone using metal plates, screws and nails (orthopedic fixation). Orthopedic fixation can relieve pain and improve function. Often, radiation therapy is given when you have healed after surgery.
- Surgery to inject a bone with cement. Bones that can’t be easily reinforced with metal plates or screws, such as pelvic bones and bones in the spine, may benefit from bone cement. Doctors inject bone cement into a bone that is broken or damaged by bone metastasis. This procedure can reduce pain.
- Surgery to repair a broken bone. If bone metastasis has caused a bone to break, surgeons may work to repair the bone. This involves using metal plates, screws and nails to stabilize the bone.
Joint replacement, such as a hip replacement, may be another option. In general, broken bones caused by bone metastasis aren’t helped by placing a cast on the broken bone.
Heating and freezing cancer cells
Procedures to kill cancer cells with heat or cold may help control pain. These procedures may be an option if you have one or two areas of bone metastasis and aren’t helped by other treatments.
During a procedure called radiofrequency ablation, a needle containing an electric probe is inserted into the bone tumor. Electricity passes through the probe and heats the surrounding tissue. The tissue is allowed to cool down, and the process is repeated.
A similar procedure called cryoablation freezes the tumor and then allows it to thaw. The process is repeated multiple times.
Side effects can include damage to nearby structures, such as nerves, and damage to bones that can increase the risk of a broken bone.
For people with multiple bone metastases, a form of radiation called radiopharmaceuticals can be given through a vein. Radiopharmaceuticals use low levels of radioactive material that has a strong attraction to bones. Once in your body, the particles travel to the areas of bone metastasis and release their radiation.
Radiopharmaceuticals can help control pain caused by bone metastasis. Side effects can include damage to the bone marrow, which can lead to low blood cell counts.
Clinical trials are studies of new treatments and new ways of using existing treatments. Enrolling in a clinical trial gives you the chance to try the latest treatments. But a cure isn’t guaranteed, and the side effects of new treatments may not be known. Discuss the available clinical trials with your doctor.
A physical therapist can work with you to devise a plan that will help you increase your strength and improve your mobility. A physical therapist may suggest assistive devices to help you cope. Examples might include crutches or a walker to take weight off an affected bone while walking, a cane to improve balance, or a brace to stabilize the spine.
A physical therapist may also suggest specific exercises to help you keep your strength up and reduce your pain.