The process of bone metastasis consists of several distinct but essential events: escape from the original site, dissemination through blood vessels, and growth at a bone. Tumor cells cross basement membranes as they initially invade vascular beds during the dissemination. The inva sion of tumor cells through basement membranes involves three distinct events: attachment of the tumor cells to the basement membrane, secretion of MMPs by tumor cells which causes degradation of the adjacent basement membrane, and migration of the cells into the target tissue. Bone metastases are frequently associated with osteolysis, which leads to pathologic frac tures and hypercalcemia, while metastasis from prostatic carcinoma usually shows osteosclerotic changes. Cancer cells promote osteolysis by activating osteoclasts through a variety of chemical mediators secreted by cancer cells themselves or by monocytes. The risk of pathological frac ture is high if lytic metastasis involves cortical destruction.
When skeletal metastasis is suspected following a roentgenogram, we suggest that a bone scintigram be performed primarily in order to identify whether the lesion is single or multiple. Patients with multiple skeletal metastases usually do not undergo surgery. Instead, radiation or chemotherapy is indicated. Surgery for skeletal metastasis does not necessarily affect the life expectancies of patients. However, if dramatic improvement in the quality of patients' lives can be expected, surgery for long bone metastasis or spinal metastasis is indicated.
For patients with long bone metastasis, we prefer to carry out resection with a wide margin before a pathological fracture occurs, since the fracture carries the risk of disseminating tumor cells. Reconstruction after the resection of long bone involving metastasis may be best achieved by prosthetic replacement. The spine is the most common site of skeletal metastasis, irrespective of the primary tumor. When patients with spinal metastasis are expected to survive longer than six months, and neurological deficits become evident in addition to back pain, decompression followed by posterior stabilization is indicated.
