This review suggests that existing theories of carcinogenesis provide much of the necessary framework for understanding the etiologies of malignant gliomas. Most of the environmental risk factors associated with brain tumors involve exposures to infectious, chemical, or physical agents capable of inflicting genetic damage. It is equally important to recognize that some potential risk factors for brain tumors, if their association proves causal, suggest as yet unknown or undefined mechanisms of carcinogenesis. For example, the mechanisms through which extremely-low-frequency electromagnetic fields might induce cancer are unknown, but interest in this area is intensifying [165].
Large population based studies currently being conducted throughout the world will help to estimate the relative importance of some suspected factors. Several of the most serious limitations of previous studies can be overcome by careful study design including sample size planning to ensure adequate power for important hypotheses and subgroup analyses, systematic pathology review to enable analyses by histologie type, collecting sufficiently detailed exposure data to minimize recall problems and permit flexibility in classifications, and using rapid case ascertainment systems to minimize the need for interviews with proxies and concomitant reporting bias. Furthermore, as important genes for brain tumors are identified, they can be used to further refine subtype classifications and to improve sensitivity in the search for environmental culprits.
Key words brain neoplasms - gliomas - environmental factors - ionizing radiation - chemical carcinogens - viruses - extremely-low-frequency electromagnetic fields