Epidemiology of Primary Brain Tumors

Abstract

It was estimated that in 1999, 16,800 individuals in the United States would be diagnosed with a malignant primary nervous system tumor and 13,100 of these would die from the disease (Landis 1999). When benign as well as malignant brain tumors are included, the incidence is over twice that for malignant brain tumors alone [34,345 individuals werenewly diagnosed with a benign or malignant nervous system tumor in 1998 (CBTRUS 1998)]. Only about half of the patients with malignant brain tumors are still alive 1 year after diagnosis (Davis1999). Although the incidence of brain tumors, particularly the more lethal subtypes, increased in recent decades (Greig et al. 1990; Modan et al. 1992; Desmeules et al. 1992), it appears that trends in childhood brain tumors (Smith 1998; Black 1998) and adult tumors (Legler et al. 1999) increased due to the introduction of diagnostic improvements, including computerized tomography (CT) scans in the mid-1970s and magnetic resonance imaging (MRI) in the mid-1980s. This issue and the recent explosion of epidemiologic and molecular genetic studies of brain tumors has focused attention on this important human cancer, which up until only a few decades ago was relatively little studied. Despite this surge of interest, the etiology of the majority of nervous system tumors remains unknown. Inherited syndromes that predispose affected individuals to brain tumor development and/or the presence of nervous system tumors in other family members appear to be present in fewer than 5% of brain tumor patients. Some environmental agents, in particular ionizing radiation, are clearly implicated in the etiology of brain tumors, but also appear to account for few cases. Numerous other physical, chemical, and infectious agents that have long been suspected risk factors have not yet been established as etiologically relevant.