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Metastatic Bone Tumors
Any cancer may metastasize to bone, but metastases from carcinomas are the most common, particularly those arising in the following areas:
Prostate cancer in men and breast cancer in women are the most common types of cancers. Lung cancer is the most common cause of cancer death in both sexes. Breast cancer is the most common cancer to metastasize to bone. Any bone may be involved with metastases. Metastatic disease does not commonly spread to bone below the mid forearm or mid calf, but when it occurs in those sites, it results most often from lung or sometimes kidney cancer.
Metastatic bone tumors are considered in all patients with unexplained bone pain, but particularly in patients who have
Prostate cancer is most often blastic, lung cancer is most often lytic, and breast cancer may be blastic or lytic.
CT and MRI are highly sensitive for specific metastases. However, if metastases are suspected, a radionuclide whole-body scan, which is not quite as sensitive, is usually done. Bone scan is more sensitive for early and asymptomatic bone metastases than plain x-rays and can be used to scan the entire body. Lesions on the scan are usually presumed to be metastases if the patient has a known primary cancer. Metastases should be suspected in patients who have multiple lesions on bone scan. Although metastases are suspected in patients with known cancer and a single bone lesion, the lesion may not be a metastasis; thus, a needle biopsy of the lesion is often done to confirm the diagnosis of a metastasis. PET for almost whole-body scanning is now often used for some tumors; it is more specific for bone metastases than is radionuclide bone scan and can identify many extraskeletal metastases.
If bone metastases are suspected because multiple lytic lesions are found, assessment for the primary tumor can begin with clinical evaluation for primary cancers (particularly focused on the breast, prostate, and thyroid), chest x-ray, mammography, and measurement of prostate-specific antigen level. Initial CT of the chest, abdomen, and pelvis may also reveal the primary tumor. However, bone biopsy, especially fine-needle or core biopsy, is necessary if metastatic tumor is suspected and the primary tumor has not been otherwise diagnosed. Biopsy with use of immunohistologic stains may give clues to the primary tumor type.
Treatment depends on the type of tissue involved (which organ tissue type). Radiation therapy, combined with selected chemotherapeutic or hormonal drugs, is the most common treatment modality. Early use of radiation (30 Gy) and bisphosphonates (eg, zoledronate, pamidronate) slows bone destruction. Some tumors are more likely to heal after radiation therapy; eg, blastic lesions of prostate and breast cancer are more likely to heal than lytic destructive lesions of lung cancer and renal cell carcinoma. Drugs used to treat receptor activator of nuclear factor kappa-B ligand (RANKL) are now being used to reduce bone destruction.
If bone destruction is extensive, resulting in imminent or actual pathologic fracture, surgical fixation or resection and reconstruction may be required to provide stabilization and help minimize morbidity. When the primary cancer has been removed and only a single bone metastasis remains (especially if the metastatic lesion appears ≥ 1 yr after the primary tumor), en bloc excision sometimes combined with radiation therapy, chemotherapy, or both rarely may be curative. Insertion of methyl methacrylate into the spine (kyphoplasty or vertebraplasty) relieves pain and expands and stabilizes compression fractures that do not have epidural soft-tissue extension.
Carcinomas of breast, lung, and prostate are the most common sources of metastatic bone tumors.
Bone metastases should be suspected in patients with known cancer, when pain is at more than one site, and/or when findings on imaging studies suggest metastases.
Bone biopsy is needed if the primary tumor is unknown after clinical and radiographic evaluation.
Most often, radiation therapy and a bisphosphonate are used to slow bone destruction.
Pathologic fractures may require treatment with surgery, kyphoplasty, or vertebraplasty.
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