Bones, lungs, and the liver are the most common places for cancer cells to spread, or "metastasize."
Once in the bone, these cancer cells can form new metastatic tumors. Do you then have bone cancer? No. You still have the type of cancer you were diagnosed with, except now it is metastatic. For example, breast cancer that spreads is known as "metastatic breast cancer." Metastatic cancers in the bone are also called bone metastases, or bone "mets."
Here are the types of cancer that are most likely to metastasize to the bone and what treatments can provide relief.
Bone Metastasis: Cancers that Commonly Spread to Bone
Bone metastasis is more likely with cancers such as:
About three out of four cases of bone metastasis result from tumors in the breast, prostate, lung, or kidney. Almost 70% of people with advanced breast or prostate cancer have bone metastasis; bone is commonly the third most common organ affected by metastases, after the lung and liver.
How and Why Cancers Metastasize to Bones
The spread of cancer to bone is a complex process that doctors are just beginning to understand. Metastasis typically involves the following process:
Cancer cells invade normal tissue nearby, then move through the walls of nearby lymph or blood vessels and begin circulating through the lymphatic system and bloodstream to reach other parts of the body. After stopping in small blood vessels at a further location, they invade the blood vessel walls and migrate into surrounding tissue where they multiply and form smaller tumors. Those new tumors need a blood supply for continued growth, so they stimulate the growth of new blood vessels.
Once they've reached the bone, cancer cells must avoid attacks from the body's immune system. So they may go through more changes. This means the new tumor may be somewhat different from the primary tumor. This can make it more difficult to treat.
Why and Where Tumors Form in Bones
The type of cancer may have something to do with why tumors form in bones. Certain cancers may release proteins that affect how a tumor forms.
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:
- Spine
- Pelvis
- Ribs
- Upper arms
- Thighs
Bone Metastasis and Its Symptoms
In some cases, areas of bone are destroyed (osteolytic). In other cases, new bone may form in response to bone metastasis (osteoblastic).
In many cases of cancer such as breast cancer, either - or both -- bone destruction and new bone formation may occur.
Bone mets symptoms include:
- Bone pain is the most common symptom, and many patients with bone metastasis experience significant pain at some point in the course of their disease.
- Broken bones, as a result of weakening from the metastasis
- Loss of appetite, nausea, extreme thirst, and other symptoms from excess calcium in the blood; as bone becomes destroyed by the metastatic tumor, the bone releases calcium into the bloodstream.
- Neurologic symptoms are not uncommon in patients with metastases of the vertebra, causing spinal cord compression or sinstability. This can cause nerve symptoms of numbness, weakness, urinary problems, and paralysis.
Treating the Primary Cancer
Most bone metastasis cannot be cured. But treatment can often help relieve symptoms.
The kind of treatment your doctor recommends depends, in part, on what kind of primary cancer you have. Other factors include:
- Which bones the cancer has invaded
- Damage to the bones
- Which treatments you have already had
- Your state of health
In most cases, doctors treat bone metastasis by treating the primary cancer. Chemotherapy and hormone therapy are examples of treatments commonly used to treat the primary cancer. These are systemic treatments, so they can travel through the bloodstream to reach different parts of the body.
Bone Metastasis Treatments That Can Help You Feel Better
These treatments for the bone can help relieve bone metastasis pain and other symptoms:
- Radiation therapy. High-energy X-rays can kill cancer cells or slow their growth. Alone or combined with other treatments, this can relieve symptoms of bone mets.
- Radiopharmaceuticals. Used only for cancer that spreads to bone, these are drugs with radioactive elements. When they are injected, they go to the bone with cancer, killing cancer cells and helping to relieve pain. Low blood counts can be a side effect of this type of therapy.
- Ablation. In this method, a needle is put directly into a tumor to destroy it with heat, cold, electric current, or alcohol.
- MRI-Guided Focused Ultrasound. This is a noninvasive procedure that uses ultrasound energy guided by MRI scanning to destroy nerve endings in the area of the tumor. The procedure is used to relieve pain in people who have not had success with radiation or who are unable to be treated with radiation.
- Bisphosphonates (Aredia and Zometa). Given intravenously (IV) for bone mets, these drugs can reduce damage to the bone, lower the risk of breaks, reduce high blood calcium levels, and lessen pain.
- Denosumab (Xgeva). Similar to bisphosphonates, this drug is injected to help keep bone from breaking down.
- Surgery. If bone damage is severe, inserting a supportive rod may be a good option. Other types of surgery may relieve pressure on the spinal cord.
- Injections of bone cement. These can also strengthen bones to prevent breaks.
Your options for treatment of bone mets may vary depending on your type of cancer, your condition, and tolerance of possible side effects.