Definition and Overview

Bone metastasis is a condition where the cancer cells have moved from the primary site and settled in any bone in the body to form new tumours. This is different from other types of cancer that begin in the bones.

Bone is one part of the body that is commonly affected by metastasis, along with liver and lung. A patient can develop more than one metastasis (where the condition is called metastases).

Bone metastasis is not a recurrence, which is characterized by the reappearance of cancer either on the same site or near it. However, there are times when the cancer is detected through its metastasis, in which it is referred to as distant recurrence.

People who have breast, kidney, thyroid, and lung cancer are more likely to develop bone metastasis than other types of cancer. The potential rate is more than 60%.

Meanwhile, men and women who experience an abnormal growth of bones (which can be detected through imaging tests) when they’re already in their old age, such as 45 years old and above, should have themselves checked for either primary or secondary cancer. Bone growth reaches its peak during the twenties and begins to decline after that.

Causes of Condition

In normal circumstances, cells divide, mature, and die to give way for new cells to form and sustain life. The process of programmed death is called apoptosis. However, some cells may end up being damaged or they become immature and behave abnormally. These cells are the ones that are vulnerable to becoming malignant or cancerous.

Since they can also divide, a single cancerous cell can eventually become a tumour and may attach itself to the tissues and blood vessels of the site where it originally forms (primary site). Though some cancer cells take many years to develop and spread, others are very aggressive.

Cancer cells that have already invaded the blood vessels can eventually reach the bloodstream (or the lymphatic system). They can travel around the body until they rest in a particular area (secondary site) such as the bones.

Once cancer has already metastasized, the chances of survival significantly drop as metastasis to the bones doesn’t have any cure. The only option is to delay the growth or stop the progression of the disease, as well as to make the symptoms more manageable through medications, surgery, and non-surgical treatment such as chemotherapy and radiation therapy.

Key Symptoms

Compared to other types of metastases, especially to the lungs and liver, bone metastasis is more prominent due to its symptoms. These include:

  • Compression of the spinal cord
  • Vulnerability to fractures
  • Pain (which can range from dull to excruciating)
  • Elevated levels of calcium in the blood

These symptoms occur either due to the damage or destruction of the osteolytic cells, one of the cells found in the bone. This means that the bone minerals are already dissolving. The other possible outcome is the formation of a new bone. Since the bone has developed due to the proliferation of the cancer cells, it can grow abnormally and thus the bone becomes deformed. This can also be described as having a denser bone mass. Normally, though, it’s a combination of the two.

Who to See and Treatments Available

Oncologists (specialists who treat cancer) monitor potential bone metastasis especially if the patient is considered a high risk. Nevertheless, they are normally detected through the personal observation and feeling of the patient and imaging tests ranging from X-rays to CT, PET, and MRI scans.

There’s no single treatment for bone metastasis. Rather, it’s often a combination of several modes to stop the growth as quickly as possible. Patients therefore are provided with good pain medications such as ibuprofen. Should the pain gets worse, the doctor may eventually provide morphine. Medications used for treating osteoporosis are also typically part of the treatment.

Standard cancer treatments such as chemotherapy and radiation therapy may also help manage the condition. In chemotherapy, a drug or a cocktail of drugs are delivered through the body, eventually killing cells, including cancerous cells. Meanwhile, radiation therapy uses gamma or X-rays to get rid of malignant cells.

New types of treatment are now being looked into to reduce pain in patients. These include complementing chemotherapy with drugs such as bisphosphonates, which prevent the breakdown of the bones.

Surgery is also another option, and it’s usually performed to keep the bone’s stability and prevent fractures. Appliances such as screws and plates may also be used.

The abovementioned treatments carry different risks. For example, standard chemotherapy can eliminate even normal cells, which can compromise the patient’s immunity while surgery can lead to infections. Radiation therapy, on the other hand, may lead to burns in targeted areas.

The doctor along with the patient should assess carefully whether the benefits of the treatment outweigh the risks. Otherwise, the patient may move on to palliative care where the goal is to minimize the strength of the symptoms and maintain the patient’s quality of life.

References:

  • Coleman RE, Holen I. Bone metastases. In: Niederhuber JE, Armitage JO, Doroshow JH, et al., eds. Abeloff's Clinical Oncology. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2013:chap 51.

  • Heck RK Jr. Benighn/aggressive tumours of bone. In: Canale ST, Beaty JH, eds. Campbell's Operative Orthopaedics. Philadelphia, Pa: Elsevier Mosby; 2012:chap 26.

  • National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines): Bone cancer. Version 1.2014. Available at: http://www.nccn.org/professionals/physician_gls/pdf/bone.pdf. Accessed: March 23, 2014.

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