Causes
A number of defective genes are involved in the cancer process. Genes that cause cancer proliferation (called oncogenes) and those that normally suppress tumors but are defective (tumor suppressor genes) may play separate roles in a step-by-step process leading to primary brain cancer. Several avenues of investigation are in progress to determine both basic causes and the triggers for such genetic defects.
Specific Genetic Abnormalities. A number of specific brain tumors, including glioblastomas, anaplastic astrocytomas, and medulloblastomas, are the result of abnormal or missing genes:
- For example, researchers have discovered a defective gene MMAC1 (Mutated Multiple Advanced Cancers) in the majority of the glioblastomas (although not low-grade gliomas). The MMAC1 gene determines how aggressive a tumor will be.
- Another defective gene, known as the Patched 2 gene, which appears to promote tumor growth, has been found in about half of all medulloblastomas.
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Inherited Genetic Factors. A large population study reported that family clusters of brain cancer occurred in a small fraction of astrocytomas, indicating that inherited factors may play a direct role in some cases.
Acquired Genetic Defects. Genetic abnormalities that cause brain tumors are not usually inherited but mostly occur as a result of environmental insults or other factors that affect genetic materials (DNA) in the cells. Researchers are studying a number of environmental assaults that might trigger brain tumors in susceptible individuals. Among them are the following:
- Abnormal development in the womb.
- Viruses.
- Hormones.
- Chemicals.
- Ionizing radiation.
- Electromagnetic fields.
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