Spinal metastasis is common in patients with cancer. The spine is the third most common site for cancer cells to metastasize, following the lung and the liver. This amounts to 70% of all osseous metastases. Approximately 5–30% of patients with systemic cancer will have spinal metastasis; some studies have estimated that 30–70% of patients with a primary tumor have spinal metastatic disease at autopsy. Spinal metastases are slightly more common in men than in women and in adults aged 40–65 years than in others. Fortunately, only 10% of these patients are symptomatic, and approximately 94–98% of those patients present with epidural and/or vertebral involvement. Intradural extramedullary and intramedullary seeding of systemic cancer is unusual; they account for 5–6% and 0.5–1% of spinal metastases, respectively.
Spread from primary tumors is mainly by the arterial route. Retrograde spread through the Batson plexus during Valsalva maneuver is postulated. Direct invasion through the intervertebral foramina can also occur. Besides the mass effect, an epidural mass can cause cord distortion, resulting in demyelination or axonal destruction. Vascular compromise produces venous congestion and vasogenic edema of the spinal cord, resulting in venous infarction and hemorrhage.
About 70% of symptomatic lesions are found in the thoracic region of the spine, particularly at the level of T4-T7. Of the remainder, 20% are found in the lumbar region and 10% are found in the cervical spine. More than 50% of patients with spinal metastasis have several levels of involvement. About 10-38% of patients have involvement of several noncontiguous segments. Intramural and intramedullary metastases are not as common as those of the vertebral body and the epidural space. Isolated epidural involvement accounts for less than 10% of cases; it is particularly common in lymphoma and renal cell carcinoma. Most of the lesions are localized at the anterior portion of the vertebral body (60%). In 30% of cases, the lesion infiltrates the pedicle or lamina. A few patients have disease in both posterior and anterior parts of the spine.
Primary sources of spinal metastatic disease include the following:
Lung - 31%
Breast - 24%
GI tract - 9%
Prostate - 8%
Lymphoma - 6%
Melanoma - 4%
Unknown - 2%
Kidney - 1%
Others including multiple myeloma - 13%
The outcome of metastatic disease to the spine and associated structures is uniformly bleak.  Median survival of patients with spinal metastatic disease is 10 months.
Spinal metastasis is one of the leading causes of morbidity in cancer patients. It causes pain, fracture, mechanical instability, or neurological deficits such as paralysis and/or bowel and bladder dysfunction. The latter compromises the quality of life of patients with cancer and puts an additional burden on their caregivers. Cord compression is normally seen as a pre-terminal event. Median survival at that stage is about 3 months.