The two types of bone cancer are primary and secondary. Primary bone cancer originates in the bone or tissues adjoined to the bone such as connective tissue. Secondary bone cancers, also known as bone metastases, are cancers that originated in another place in the body and then spread to the bone. The cells in bone metastases resemble the cells from the cancer’s origin. They are not bone cells that have become cancerous, as in the case of primary bone cancers.
Primary bone cancers: The most common types of primary bone cancers include Osteosarcoma, Chondrosarcoma, and Ewing’s sarcoma. Osteosarcoma develops in new tissue of growing bones and occurs most commonly in children or adolescents. Chondrosarcoma originates in cartilage, which is a type of connective tissue that serves as a protective layer between bones ends. Ewing ‘s sarcoma originates in immature nerve tissue within bone marrow. This type of bone cancer also occurs more frequently in children and adolescents. Less common bone cancers include malignant fibrous histocytoma and fibrosarcoma. These cancers are similar to Osteosarcoma in that they occur mainly in the extremities, except they occur in adults.
Cancers Metastatic to Bone or (Secondary bone cancers): Although most cancers can spread to or invade bone, the most common cancers that spread to bone are multiple myeloma, breast, prostate, lung, kidney, and thyroid cancer. The ribs, pelvis and spine are normally the first bones impacted by bone metastases, while bones more distant from the central skeleton are less frequently affected. It is not well understood why certain cancers metastasize to bone more than others. However, some general observations about bone metastases are as follows:
- Breast cancer is the most common type of cancer to spread to bone, followed by prostate, then lung.
- Carcinomas, or cancers that arise from tissues that line or cover organs, are much more likely to metastasize to bone than sarcomas, cancers that originate in connective tissue (cartilage, fat, or muscle).
- Bone metastases from kidney cancer may occur many years after the primary cancer has been treated.
Signs and Symptoms of Bone Cancer
The first symptom of bone cancer is usually pain or tenderness near the cancer. Bone pain is caused by stretching of the periosteum (thick membrane that covers bone) by the cancer, or by stimulation of nerves within the bone. Bone pain may be hard to differentiate from ordinary low back pain or arthritis. Usually the pain due to bone metastasis is fairly constant, even at night. It can be worse in different positions, such as standing up, which may compress the cancer in a weight bearing bone. If pain lasts for more than a week or two, doesn’t seem to be going away, and is unlike other pain that may have been experienced, it should be evaluated by a physician.
A patient may also experience a pathological fracture as the first sign of bone cancer. A pathological fracture is a break in a bone due to problems within the bone itself rather than by external factors, such as force. Pathological fractures are caused when the cancer destroys enough bone that the skeleton can no longer support normal body functions adequately.
Diagnosing Bone Cancer
Bone cancer may be evaluated by the use of either radiological tests, surgical biopsy, or blood tests.
Radiological tests, including X-ray, bone scan, and skeletal survey, remain the best method for evaluating cancer in the bones.
- X-ray: When a patient experiences pain that is suspected to be a result of bone cancer, the first step in diagnosis is usually to X-ray the area near the pain. When enough of the healthy bone in any area is worn away by metastatic lesions, the damaged area will show up as a dark spot on the X-ray that look like holes in the bones.
- Bone Scan: A more comprehensive test used to diagnose bone cancer is a type of X-ray called a bone scan. In this test, low level radioactive particles are injected into a vein. They circulate through the body and are selectively picked up by the bones. A high concentration of these radioactive particles indicates the presence of rapidly growing cancer cells.
- Skeletal Survey: In order to diagnose blastic lesions, or lesions where extra bone has built up, a skeletal survey may be utilized. This is a form of X-ray. Normally an X-ray is selective for a particular area of concern, but with a skeletal survey, all areas are imaged. All patients with multiple myeloma and many with breast cancer undergo a skeletal survey to detect bone metastases that have not yet developed observable symptoms.
- Other: Occasionally, other radiological procedures may be used to assess bone cancer, such as a computed axial tomography (CAT) scan, magnetic resonance imaging (MRI) scan, or PET scan.
Either a needle biopsy or an incisional biopsy may also be useful for diagnosing bone cancer. During a needle biopsy, the surgeon makes a small hole in the bone and removes a sample of tissue from the tumor with a needle-like instrument. In an incisional biopsy, the surgeon cuts into the tumor and removes a sample of tissue. The tissue is then examined under a microscope to determine whether it is cancerous. Biopsies are best done by orthopedic oncologists—doctors experienced in the diagnosis of cancer involving the bone.
The early detection of bone cancer is important for effective management. In the past, pain and fractures were often the first signs of cancer involving bones. Unfortunately, by the time these signs occur, the cancer cells are already present and have begun to impact the patients overall bone health. Relying on these signs typically results in a late diagnosis of bone cancer. Blood tests that can detect the presence of bone cancers before they manifest in pain or fractures may be useful for identifying patients that would benefit from treatment before complications develop.
Cancers in the bone cause an increase in bone remodeling activity. Normal bone is constantly being remodeled, or broken down and rebuilt. Cancer cells disrupt the balance between the activity of osteoclasts (cells that break down bone) and osteoblasts (cells that build bone). When cancer cells are in the bones, some proteins, genes, or byproducts from the building blocks of bone are produced at a higher rate than during normal remodeling.
Measuring blood levels of these substances, called biological markers, can be useful for diagnosing cancer involving the bones. Higher levels can indicate that a cancer has progressed. Though most biological markers are not routinely used for the diagnosis of bone cancers at this time, some are very useful, while others show promise for the future.
Bone specific alkaline phosphatase (BSAP) is an enzyme that is present in the cells that participate in bone formation, called osteoblasts. BSAP has been used for many years to detect increases in bone formation activity. Blood levels of BSAP are increased in patients with bone cancer and other conditions that result in increased bone remodeling. Increases in BSAP have been detected in patients with bone metastasis caused by prostate cancer, and to a lesser degree, in bone metastases from breast cancer. Unfortunately, BSAP is not completely specific for cancer because alkaline phosphatases are also produced by other organs and can be elevated by other conditions. Nonetheless, BSAP can be monitored in patients who are known to be at risk of bone metastases.
Other biochemical markers are under investigation, but at this time, none have been approved for use in the clinical setting.
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