One of the characteristics of cancer is that it can spread from the location where it started. This is also one of the greatest dangers of cancer. The cancer cells can spread to distant parts of the body where it continues its destruction of healthy tissue. This types of cancer spread usually indicates advanced cancer and the outlook is often poor. While the cancer cells can spread to various sites, one of the commonly affected areas is the bone.
What is bone metastasis?
Bone metastasis or metastatic bone disease is a condition characterized by the spread of cancer cells from the site where cancer originates to bone. Most cancers can spread to bone. However, cancer of some of the organs have an increased risk of bones spread. These includes breast cancer and prostate cancer. Cancer can spread to any bone but the pelvic bones and spine bones (vertebrae) are most commonly affected.
In some people bone metastasis might be the first presenting symptom or in others it may occur years after successful treatment of the primary cancer. Common presenting symptoms of bone metastasis include pain in the bone and an increased tendency of fracture following minimal trauma. Treatment options include drugs and certain surgical interventions to stabilize affected bones or repair fracture.
Bone Cancer vs Bone Metastasis
Bone cancer is one type of cancer that can occur. It is where the cancer arises from the bone. It is also referred to as primary bone cancer since the bone is the site of origin of the cancer. This is not the same as bone metastasis. In bone metastasis the cancer in the bone has originated elsehwere in the body but subsequently spreads to the bone.
Therefore the metastatic cancer in the bone has the characteristics of the tissue where it originated. It is also referred to as seconary cancer. However, when cancer originates in the bone then it has charactertistics of bone tissue. Similarly this can metastasize and lodge in other organs.
Signs and Symptoms
Common presenting symptoms of bone metastasis include:
- Severe pain in the bones (usually described as a deep-seated pain).
- Fractures that occur with even slight trauma due to the cancer weakening the bones.
- Nerve dysfunction when there is spinal cord compression due to collapsing vertebrae. This may presenst as an inability to control bladder and bowel activities, weakness of legs and even paralysis.
- Abnormally high level of calcium in the blood as bone is broken down. This elevated calcium levels may present with nausea, vomiting, confusion and other symptoms of hypercalcemia.
All of these symptoms often lead to deterioration of quality of life. Pain is the most common debilitating symptom. Initially patients experience a dull ache which gradually worsens over time. Even controlled pain management treatment cannot prevent episodes of breakthrough pain which may occur several times in a day.
Bone metastasis leads to lowering of the pH in the body (acidosis). Pain receptors (nociceptors) in the brain may be stimulated by acidosis and this in turn triggers pain. The cancer in the bone also impairs normal bone metabolism which can result in malformed bones with increased risk of fracture.
Causes of Bone Cancer Spread
The root cause of bone metastasis is the cancer that arises at some part of the body. Cancer occurs whenever there is unrestricted cell division and inhibition of natural cell death (apoptosis). This programmed cell death helps to remove the older cells from the body at regular interval. Mutation, which is a sudden irreversible change in the genetic material (DNA), is the reason behind the formation of cancer cells.
The exact cause that triggers these genetic mutations is not known. However, certain environmental and genetic factors are thought to be responsible. The structure of cancer cells are also not normal. It grows rapidly and invades healthy tissue as the malignancy (cancerous tumor) enlarges in size. It eventually infiltrates beyond the tissue and even the organ where it originated.
Why does cancer spread to the bone?
Cancer cells have a tendency to spread from the primary organ (where it starts) to other organs. This may occur with direct spread where the cancer infiltrates neighboring organs as it continues to invade and destroy healthy tissue. Therefore cancers that originate near bone can reach the bone. However, the cancer can also reach distant sites and this characteristic of cancer cells is known metastasis.
The cancer cells may break away from the primary site and travel through the bloodstream or lymphatic system. Different organs may be secondarily affected by cancer cells from the primary organ. Bone is often affected secondarily, although it is not clear why some cancers spread to bones and not to other organs like the liver for example since all blood passes through the liver at some point.
Cancers That Most Commonly Spread To The Bone
Primary cancers of the following organs are more likely to spread secondarily (metastasize) to the bone:
- Lymph nodes (lymphoma)
However, it is also possible that a host of other cancers can also spread to the bone. Furthermore it is important to understand that cancer can arise in bone. This is not the same as secondary bone cancer where cancer from elsewhere in the body spreads (metastasizes) to the bone.
Treatment of Bone Metastasis
Overall, the prognosis is poorer when metastasis occurs, irrespective of whether it is bone metastasis specifically. Nevertheless it should be treated and one or more of the following treatment options may be considered.
- Drugs for bone-building like bisphosphonates.
- Anticancer drugs (chemotherapeutic agents) to target and destroy cancer cells.
- Hormone drugs for certain types of cancers.
- Pain killers, ranging from milder agents like ibuprofen to stronger drugs such as morphine to manage the pain.
- Radiation therapy targeted at sites where the cancer is located to destroy the cancer cells.
- Surgery to stabilize affected bones and repair fractured bones.
Read more on hormone therapy for breast cancer.
Due to the risk of cancer recurrence and spread, it is always important that people with a past medical history of cancer undergo routine screening.