Wednesday, October 24, 2012
Spinal metastases are a prevalent problem in the cancer population. It is estimated that 20 percent of all cancer patients will develop metastases to the spine and that approximately 20,000 new cases will be diagnosed annually in the United States. The primary goals of treatment include preservation or restoration of neurologic function and spinal stability, pain relief, and durable tumor control.
Modern medicine offers myriad treatment options for spinal metastases, and these treatments can be broadly classified into three categories: systemic therapy, radiation therapy, and surgery. Systemic therapy options include various forms of chemotherapy, immunotherapy, hormonal therapy, and novel medications targeted at specific molecular receptors. Radiation therapy can be administered as conventional external-beam radiation therapy (cEBRT), as single-fraction or hypofractionated stereotactic radiosurgery (SRS), and as percutaneously placed or intraoperatively administered brachytherapy. Surgical options include kyphoplasty, instrumented stabilization, and numerous methods of tumor resection.
Treatment options for spinal metastases are numerous and constantly evolving. In order to determine the optimal combination and sequence of systemic, radiation, and surgical therapies, physicians at Memorial Sloan Kettering have devised a dynamic consideration framework that allows us to include novel therapies and keep pace with medical innovations. The framework includes four considerations about the patient’s condition: neurologic, oncologic, mechanical, and systemic (NOMS).
The neurologic consideration focuses on the presence of clinical myelopathy or radiculopathy and the extent of epidural spinal cord compression (ESCC). Patients without neurologic deficits and with tumors confined to bone or patients with epidural extension without spinal cord compression are classified as low-grade ESCC. Patients with cord compression are classified as high-grade ESCC.
The oncologic consideration focuses on tumor histology and histology-specific sensitivity to systemic and conventional fractionated radiation therapy. Tumors such as hematologic malignancies and breast and prostate carcinomas generally exhibit a consistent and durable response to cEBRT and are classified as radiosensitive. Solid tumors other than breast and lung — such as melanoma, sarcoma, and lung, renal, and colorectal carcinomas — do not consistently respond to cEBRT and are classified as radioresistant. Although radiosensitive tumors can be safely treated with cEBRT regardless of the degree of cord compression, radioresistant tumors require SRS.
In our experience, treatment of radioresistant tumors with high-dose SRS has resulted in a 96 percent rate of local control at three-year follow-up, regardless of the tumor size, histology, and previous radiation. In the absence of high-grade ESCC, patients with radioresistant metastases may be treated with SRS. However, patients with radioresistant tumors and high-grade ESCC require a surgical stabilization and decompression prior to SRS to optimize the radiation dose delivered to the tumor without risking spinal cord toxicity.
Mechanical instability of the spine results in uncontrollable pain. The character of the pain is level dependent and is generally elicited by movement. The spine instability neoplastic score (SINS) was devised in order to facilitate the determination of instability. It consists of six considerations, including the level, the quality of pain, and the extent of osteolysis, deformity, and vertebral body and posterior element involvement. Patients with gross spinal instability require stabilization that can be accomplished with vertebral cement augmentation or with percutaneous or open instrumented fixation.
Systemic considerations include the extent of metastatic tumor burden and other medical comorbidities. These factors help determine the patient’s ability to undergo surgery, radiation, and chemotherapy. This determination is generally made in concert with the patient’s medical oncologist and internist and may require additional staging and risk-stratification studies.
The NOMS framework was developed based on the experience of the spinal oncology team at Memorial Sloan Kettering. The indications for surgery, radiation, and systemic therapy are based on systematic examination of relevant literature and several recommendations from a panel of experts. The framework readily allows incorporation of new treatment modalities, while keeping in focus the primary goals of treating spinal metastases.