Bone metastases are a frequent complication in patients with advanced cancer. Skeletal involvement is most common in patients with metastatic breast or prostate cancer, but bone is a frequent site of metastases in most advanced malignancies . Although the overall incidence of bone metastasis is not known, over one-half of people who die of cancer in the United States each year are thought to have bone involvement .
Bone metastases can cause a wide range of symptoms that can impair the quality of life or shorten survival. Direct complications of bone involvement include severe pain, pathologic fractures, and epidural spinal cord compression . In addition to these local effects, osteolytic metastases can result in life-threatening hypercalcemia. (See "Overview of cancer pain syndromes", section on 'Multifocal bone pain' and "Evaluation and management of complete and impending pathologic fractures in patients with metastatic bone disease, multiple myeloma, and lymphoma" and "Clinical features and diagnosis of neoplastic epidural spinal cord compression, including cauda equina syndrome" and "Hypercalcemia of malignancy".)
The mechanisms by which bone metastases develop and affect normal bone will be reviewed here. The control of normal bone remodeling is discussed separately. (See "Normal skeletal development and regulation of bone formation and resorption".)
OSTEOLYTIC VERSUS OSTEOBLASTIC BONE METASTASES
Bone metastases are generally classified as either osteolytic, characterized by destruction of normal bone, or osteoblastic, with the deposition of new bone based upon the predominant radiologic appearance. This distinction is not absolute; many patients with bone metastases have both osteolytic and osteoblastic lesions, and individual metastatic lesions can contain both osteolytic and osteoblastic components (table 1).
In both types of lesions there is a dysregulation of the normal bone remodeling process. (See "Normal skeletal development and regulation of bone formation and resorption", section on 'Bone modeling and remodeling'.)