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.
(See also Overview of Bone and Joint Tumors Overview of Bone and Joint Tumors Bone tumors may be benign or malignant. Malignant tumors may be primary or metastatic. In children, most bone tumors are primary and benign; some are malignant primary tumors (eg, osteosarcoma... read more .)
Symptoms and Signs of Metastatic Bone Tumors
Metastases manifest as bone pain, although they may remain asymptomatic for some time. Bone metastases may cause symptoms before the primary tumor is suspected or may appear in patients with a known diagnosis of cancer.
Diagnosis of Metastatic Bone Tumors
X-ray of the entire bone
Whole body radionuclide technecium-99 bone scanning to identify metastases
Advanced imaging (CT, MRI, and/or whole body PET-CT scanning for selected purposes)
Clinical evaluation and testing to diagnose the primary tumor (if unknown)
Often biopsy if the primary tumor is unknown after assessment
Metastatic bone tumors are considered in all patients with unexplained bone pain, but particularly in patients who have
Pain or radiographic abnormalities at more than one site
Findings on imaging studies that suggest metastases
Prostate cancer is most often blastic, lung cancer is most often lytic, and breast cancer may be blastic or lytic.
CT and particularly MRI are highly sensitive for specific metastases. However, if metastases are suspected, a radionuclide whole-body scan, which is not quite as sensitive or specific, 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. Whole-body PET-CT 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.
An evaluation to identify an initially unknown primary cancer in a patient with a single or multiple bony lesions includes a comprehensive history and physical examination; CT of the chest, abdomen, and pelvis; mammography in females; and prostate-specific antigen (PSA) measurement in males. Such an approach will identify the primary cancer over 85% of the time. 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. Sometimes the primary tumor cannot be identified after these tests plus PET-CT and any indicated endoscopy.
In patients who present with a fracture, especially older patients, it is important to determine if it is a pathologic fracture due to a cancer. Such a fracture may be suspected, especially if the patient has a known primary cancer. However, the fracture may be the initial manifestation of a cancer elsewhere in the body. The radiographic appearance may be destructive, suggesting a cancer, but may have only subtle abnormalities, for example, such as punctate calcifications that are easily missed may be the only findings suggesting a cancer. Also, although unusual, a bone lesion thought to be the cause of a metastatic fracture may be a fracture through a primary bone tumor such as chondrosarcoma or osteosarcoma. An atypical (age of patient or radiographic appearance) destructive "metastatic" lesion with or without fracture especially with punctate calcifications must be discriminated from the rare primary bone tumor with the help of a musculoskeletal surgical oncologist or musculoskeletal radiologist.
Treatment of Metastatic Bone Tumors
Usually radiation therapy for symptomatic or large or progressively enlarging lesions
Surgery to stabilize bone at risk of pathologic fracture or resect highly diseased bone (with joint reconstruction if needed)
Kyphoplasty or vertebraplasty for certain painful vertebral fractures
Treatment of metastatic bone tumors 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. Radiation therapy is used for lesions that are symptomatic and for larger lesions that, if they progress, risk leading to pain, fracture, and/or a more difficult stabilization procedure. Early use of radiation (ranging from single treatment 8 Gy to multiple treatments to 30 Gy) and bisphosphonates (eg, zoledronate, pamidronate) or denosumab 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. Denosumab is used to block the receptor activator of nuclear factor kappa-B ligand (RANKL) to reduce progressive bone destruction and thus treat and prevent pain and/or pathologic fractures due to metastases from a variety of primary cancers. Sometimes denosumab is indicated to also delay the presentation (ie, the initial manifestations) of skeletal metastatic disease and/or reduce skeletal-related metastatic events (ie, radiation therapy to bone, repair of impending or true patholologic fracture, spinal cord compression or malignant hypercalcemia).
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 limited bone metastasis remains (especially if the metastatic lesion appears ≥ 1 year 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, prostate, and kidney 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.
Patients with known solid organ cancer and limited bone lesions may require a needle biopsy to confirm metastatic disease and exclude a second primary tumor.
Most often, radiation therapy, bisphosphonates, and RANKL inhibitors are used to slow bone destruction.
Pathologic fractures may require treatment with surgery, kyphoplasty, or vertebraplasty.