Central nervous system disorders

VI./4.1.: Epidemiology

Metastatic brain tumors account for only a few percent of nervous system diseases, but nearly half of the mass lesions in the brain are metastatic tumors. Approximately 20% of patients with malignancies have brain metastasis on autopsy. This finding has high clinical significance because the course of the disease and its complex oncologic treatment are determined by this. Metastatic tumors are located in the brain parenchyma, meninges, spinal structures and bones (cranium and vertebrae). Solid –solitary or multiple- tumors are spread via haematogenous route while leptomeningeal carcinomatosis is caused by infiltration of the meninges in certain types of tumors.

Brain metastases most commonly originate from epithelial tumors, such as cancers of the lung (46%), breast (13%), gastrointestinal tract (9%), melanoma (3%) and genitourinary system (3%). Although small cell lung cancer is not as common as other pulmonary tumors, but it metastasizes in half of the patients. On the other hand, 40-60% of patients with the otherwise uncommon malignant melanoma will have brain metastasis, which can be explained with the shared embryonic origin (neural crest cells) and cell surface antigens. Brain metastasis originating from cancer of the prostate gland is an extreme rarity.

Brain metastases are typically (but not exclusively) located in the superficial cortical or subcortical regions of the watershed areas or in the cortico-subcortical junction. Of note renal or colorectal carcinomas tend to metastatize in the cerebellum.

Gender does not affect the incidence of brain metastatic tumors.

Most patients with brain tumors are 50-70 year old. Younger patients may have hematologic (leukemia or lymphoma) or germ cell tumors.

Brain metastasis usually present in two years after the initial diagnosis of the primary tumor but could develop many years after the complex treatment as in the case of some breast cancers.