Brain Metastasis from Solid Tumors

Brain metastases occur in roughly 15% of all cancer patients, although autopsy analyses have shown that the incidence is as high as 30% in patients with breast cancer, 40% in those with lung cancer, and 75% in those with melanoma. Moreover, the incidence of brain metastasis has increased as imaging techniques have improved to allow smaller, subclinical lesions to be detected and extracranial systemic therapy has become effective enough that only the central nervous system (CNS) is left as a potential site for distant spread.Of great importance is the role of the blood-brain barrier (BBB), which protects the CNS from toxic substances, foreign pathogens, and metastatic cells. However, research has shown that certain primary neoplasms can damage the BBB, thus allowing the neoplasm to spread to the CNS. Once these metastatic CNS deposits have crossed the BBB, they are protected from chemotherapy because the BBB repairs itself.Currently, magnetic resonance imaging is the diagnostic test of choice for detecting intracranial lesions, although computed tomographic scans are used in the acute setting to rule out life-threatening complications. In addition, novel techniques involving the use of radiolabeled glucose and amino acids are gaining popularity for better evaluation of intracranial metastases.Prognostic factors differ among various types of primary tumors, but classification systems exist to guide clinical decision making. The retrospective recursive partitioning analysis, score index for radiosurgery, and basic score for brain metastasis measures are used to inform clinicians of patients' long-term prognosis and to identify which patients should receive aggressive treatment and which should receive palliative care.Numerous treatment options exist for patients with brain metastasis, although side effects are common. Isolated chemotherapy has been shown to be largely ineffective, and recent research has documented impaired cognitive function in patients who undergo this treatment. Similarly, risks and long-term effects associated with more invasive therapy, such as surgery, whole-brain radiotherapy, stereotactic radiosurgery, and the combination of multiple treatment modalities, have been extensively studied. Still, the standard of care for patients with brain metastasis is a combination of chemotherapy and radiotherapy to provide the best treatment for symptoms and chances of long-term survival.Prophylactic cranial irradiation is now being used to reduce the incidence of brain metastasis, especially in patients with breast or lung cancer or melanoma, which are known to spread to the CNS early. Extensive research is underway to develop chemotherapeutic agents that are better able to traverse the BBB.