Each year, about 100,000 Americans with cancer find out that the cancer has spread to their bones. This is called bone metastasis, or "bone mets," and it's different from cancer that starts in the bone. Cancer that leads to bone metastasis may have started in your breast, your prostate, your lungs, or other parts of your body.
Odds are, bone pain brought this metastasis to your attention. You may wonder how this could have happened, especially if you received early, aggressive treatment for your cancer and any "renegade" cancer cells. And you may wonder what's on the horizon for you.
Cancer that has metastasized to the bone is incurable but treatable. A wide array of treatments can ease pain and slow its progression. Read on to learn what is going on inside your body and what you can expect with treatment.
How Cancer Spreads to Bone
"Bone metastases can be a difficult concept to grasp," says Julie Fasano, MD, a medical oncologist with Memorial Sloan-Kettering Cancer Center's Commack Facility in Long Island, N.Y. Although it usually shows up within two to three years of diagnosis, it can appear many years later, she says. Sometimes, it doesn't cause any symptoms.
How does it happen? Metastasis can occur when cancer cells break away from the primary tumor, where the cancer began. The cells may then enter the bloodstream or lymph system and travel to the bone marrow. "The matrix of the bone marrow secretes cytokines," Fasano says. These proteins may attract cancer cells.
Cancer cells can remain hidden and inactive in bone for a long time. This means they can evade treatment. At some point, however, the cells may begin to multiply and grow new blood vessels to obtain oxygen and food. This allows a tumor or tumors to form.
Scientists are just beginning to understand what happens in the bone to prompt this process, Fasano says. Once metastasis begins, there may be a "vicious, self-perpetuating cycle." The release of cytokines may attract yet more cancer cells to the bone marrow, and this may help cancer cells survive.
Signs and Symptoms of Bone Metastasis
Bone metastasis can cause major pain. "It is more painful in a weight-bearing bone than in other bones," Fasano says. For example, a metastasis in the hipbone might be more painful than one in a rib bone.
At first, it may be hard to tell what's causing your symptoms. "And it may be hard to remember that not all pain is caused by the cancer," Fasano says. So it's important to tell your doctor right away if you have any of these symptoms of bone metastasis:
- Bone pain. This is often the first symptom of bone mets. It may come and go at first. It is often worse at night and gets better with movement. However, over time, the pain doesn't go away.
- Broken bones. This occurs because bone metastases weaken bone and puts you at risk for fracture. Breaks are most common in the leg, arm, or a bone in the spine.
- Numbness, paralysis, or trouble urinating. Pressure on the spinal cord from bone metastases in the spine can cause this.
- Loss of appetite, nausea, extreme thirst, confusion, or tiredness. These symptoms may be due to high levels of calcium in the blood. As metastasis develops in the bone, there is release of calcium into the bloodstream.
If you have symptoms, your doctor will likely want to do a thorough physical exam, blood tests, and a bone scan. Depending upon the lab test results and where and how severe the bone pain is, Fasano says she often orders an X-ray or a PET or CT scan. To confirm the diagnosis, the doctor may take a biopsy of tissue to look at under a microscope.
Types of Treatment for Bone Metastasis
How doctors treat bone metastasis depends on the extent and location of the bony lesions, Fasano says. Treatments include:
- Treating the underlying cancer. This is the most important step, Fasano tells WebMD. Treatment depends on the type of tumor and where it started in your body. Treatment often includes a combination of drugs that were used to treat the primary cancer when you were first diagnosed.
- Bisphosphonates. Bisphosphonate drugs such as Aredia and Zometa help prevent the breakdown of bone, which can ease pain and reduce your risk of fractures. Doctors will infuse bisphosphonates through an IV "every four weeks to halt or slow the progression of metastasis formation and to help prevent breaks," says Fasano.
Bisphosphonate therapy is especially important if the metastasis is in a weight-bearing bone or is causing a great deal of pain. If metastasis in the spine is causing severe pain and risking a collapse of vertebrae, Fasano sends the patient for an orthopedic evaluation. For elevated calcium levels, patients will often need intravenous fluids, bisphosphonates, and other medications to help lower levels.
- Denosumab (Xgeva). Denosumab is injected under the skin, rather than by infusion, and also helps prevent bone breakdown. It's more expensive than bisphosphonates, so some insurance companies will pay for it only after you've first tried a bisphosphonate.
- Vertebroplasty. In this outpatient procedure, bone cement is injected into a fractured vertebra. The cement hardens quickly and can dramatically improve back pain within hours. "This is not a major surgery and it can make a big difference," Fasano says.
- Surgery and/or radiation. If a fracture seems likely in the near future, an orthopaedic surgeon may insert a rod or pin to stabilize the bone. "Typically, we also do a couple of radiation sessions to further stabilize the bone," Fasano says. Radiation aims high-energy X-rays at the tumor to kill the cancer. If surgery isn't needed, radiation therapy alone may ease pain. "Depending upon the location and extent of the tumors, this usually involves five to 10 sessions," she says.
Treatment for bone metastasis can prolong life and relieve symptoms. Much depends upon the type of cancer you have, how old you are, and how much time has elapsed since you first were diagnosed. "But many people can do really well for a long period of time," Fasano says.