bone cancer

bone cancer, disease characterized by uncontrolled growth of cells of the bone. Primary bone cancer—that is, cancer that arises directly in the bone—is relatively rare. In the United States, for example, only about 3,600 new cases of primary bone cancer are diagnosed each year. Most cancer that involves the bone is cancer that has spread (metastasized) from other tissues in the body through the blood or lymphatic systems. Different types of bone tissue give rise to different types of primary bone cancer. Osteosarcoma develops from cells that form the bone, and Ewing tumour of the bone (Ewing sarcoma) develops from immature nerve tissue within the bone. Both types most commonly affect males between 10 and 20 years of age. Chondrosarcoma, which forms in cartilage tissue, principally affects persons over age 50. More than one-half of the cases of primary bone cancer, even once-deadly types, can now be treated successfully.

Causes and symptoms

Only a small portion of bone cancer cases are associated with known risk factors, which include exposure to radiation or chemotherapy, Paget disease, and rare hereditary syndromes such as hereditary retinoblastoma. The majority of cases seem to occur randomly in otherwise healthy individuals.

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The most common symptom of bone cancer is pain or tenderness over the affected bone. Bone tumours often are not noticed until minor trauma causes significant pain and disability that leads to further investigation. This association has led to the mistaken conclusion that traumatic injuries can cause bone cancer. Other symptoms that can occur include bone fractures, decreased mobility of a joint, fever, fatigue, and anemia. These symptoms are not specific to bone cancer and can be the result of other, benign processes.

Diagnosis and prognosis

Preliminary investigation of a bone tumour can include a blood test for the enzyme alkaline phosphatase. As bone cancer grows, the amount of the enzyme in the blood increases dramatically, but it can also increase for other reasons. With bone cancer, unlike many other types of cancer, X-ray imaging can be very helpful in making a diagnosis. The images will show whether a tumour is creating bone tissue or destroying normal bone tissue. Images of the bone useful for making a diagnosis can also be obtained by computed tomography (CT scans), magnetic resonance imaging (MRI), and a type of radioisotope scanning commonly called a bone scan. The final diagnosis of cancer, however, requires the removal of a portion of the tumour for examination under a microscope.

The prognosis of bone cancer depends on both the type of cancer and the extent to which it has spread. Bone cancer most frequently spreads to the lungs, but it may also spread to other bones and only rarely to other tissues. Overall, the prognosis for long-term survival has improved to more than 50 percent, including cases in which the tumour has spread to other parts of the body. Of the different types of primary bone cancer, chondrosarcoma has the best prognosis and osteosarcoma the worst.

Treatment

As with many cancers, the treatment of bone cancer depends on the type of cell, location, size, and spread of the primary tumour. Most cases require a combination of surgery, chemotherapy, and radiation. In some cases, surgery requires the amputation of the involved limb. In other cases, it may be possible to remove only a portion of the bone and replace it with a prosthesis or bone graft. Chemotherapy may be given before or after surgery and is tailored to the specific type of bone cancer.

Prevention

Prevention of bone cancer will require a better understanding of its causes than is currently available. If a patient has a known risk factor for bone cancer, such as Paget disease, careful screening may help detect and treat the cancer in its early stages, thereby improving the chances for survival.