Brain tumors are abnormal growths of cells in the brain. They can be malignant (cancerous) or benign (non-cancerous). Brain tumors are relatively uncommon, accounting for less than 2% of all cancers. However, they can be very serious and in some cases fatal. Understanding the main reasons why people develop brain tumors is important for prevention, early detection, and treatment.
Genetic mutations
One of the key factors that contributes to brain tumor formation is genetic mutations. These are changes or defects in genes that control cell growth and division. Mutations cause cells to grow out of control and form a mass.
Some genetic syndromes linked to brain tumors include:
- Neurofibromatosis – This genetic disorder causes tumors to form on nerve tissues. Patients have a higher chance of developing gliomas and other brain tumors.
- Tuberous sclerosis – This condition also leads to tumor growth in multiple organs including the brain.
- Von Hippel-Lindau disease – This syndrome leads to increased risk for several tumor types including central nervous system tumors.
- Li-Fraumeni syndrome – Characterized by inherited mutations in the TP53 gene, it raises the risk of cancers like gliomas.
In many cases, genetic mutations that contribute to brain tumor formation are acquired, not inherited. Acquired mutations accumulate over the course of a lifetime. Some common acquired mutations in brain tumors affect EGFR, IDH1, PIK3CA, and PTEN genes.
Radiation exposure
Past exposure to ionizing radiation is another known contributor to brain tumor development. Sources of radiation that have been linked to brain tumors include:
- Radiotherapy – Radiation therapy used for treating conditions like leukemia or lymphoma can increase subsequent risk of a brain tumor.
- Atomic bombs – Survivors of the nuclear bombs in Japan during World War 2 had a noticeable elevation in brain tumor frequency.
- Nuclear power plant accidents – Increased brain tumor rates have been observed after nuclear power plant disasters like Chernobyl.
- Diagnostic imaging – While the risks are low, repeated CT scans or X-rays on the head/neck may contribute a small growth risk.
Ionizing radiation causes DNA damage that can lead to genetic mutations and cancerous growths over time. The risk of developing a radiation-induced brain tumor is highest 5-10 years after exposure.
Head injuries and infections
Serious head injuries have been linked to a higher risk of getting certain types of brain tumors later in life. The correlation is strongest for meningiomas, which arise from the membrane layers surrounding the brain and spinal cord.
Possible explanations for the head trauma-brain tumor connection include:
- Scar tissue formation – During healing, tissue damage from an injury triggers increased cell growth that may become tumorous over time.
- Chronic inflammation – Head injuries trigger ongoing inflammation which provides favorable conditions for cancer formation and mutations.
- Disruption of brain microenvironment – Trauma may alter signaling between cells in the brain, promoting abnormal growths.
Besides physical head trauma, certain infections are tied to brain tumor formation including:
- HHV-6 – Human herpesvirus 6 infection is positively associated with glioma risk.
- HIV – Brain lymphoma risk is higher in people with HIV/AIDS.
- EBV – Epstein-Barr virus is connected to CNS lymphomas that arise from white blood cells.
- Parasitic infections – Chronic neurocysticercosis seems to predispose to gliomas.
Infections likely contribute by triggering prolonged inflammation and cell damage. The immune system response against infections may also play a role.
Environmental and occupational exposures
Exposure to certain chemicals, metals, and other agents may influence brain tumor development as well. Some links include:
- Pesticides – Insecticides, herbicides, and fungicides are suspect carcinogens that may be implicated in glioma and astrocytoma risk.
- Solvents – Organic solvents like benzene and formaldehyde used in various industrial applications could contribute to brain cancer.
- Air pollution – Particulate matter and other pollution sources may be possible co-factors for brain tumor formation.
- Non-ionizing radiation – Very high exposures to radiofrequency radiation like from cell phones may have a small tumor growth influence.
Workplace exposures are particularly relevant. Studies indicate modestly higher brain cancer rates in workers in industries like petrochemical plants, aerospace manufacturing, rubber production, and nuclear facilities. The effects are likely due to chemical exposures.
Lifestyle factors
While less is proven about lifestyle influences, some habitual factors may impact brain tumor risk to a small extent:
- Smoking – Long-term heavy smoking seems to correlate with higher meningioma rates.
- Diet – Diets high in processed meats and nitrates are associated with glioma risk.
- Obesity – Increased body fatness may contribute slightly to meningioma development.
- Alcohol – Heavy drinking may heighten risk, perhaps due to its relationship with inflammation and immunosuppression.
The effects of smoking, diet, and other lifestyle factors are modest. But they may work together with other risk factors to collectively influence brain tumor formation.
Age
Age is one of the strongest predictors of brain tumor risk. These growths become more common as people get older. Reasons include:
- Time for mutations to accumulate – Genetic errors increase over decades, raising cancer risk.
- Reduced DNA repair – Aging cells lose their ability to fix DNA damage from mutations or toxins.
- Weakened immune function – This allows mutant cells to more easily evade destruction.
Altered brain microenvironment – Changes to signaling between brain cells occurs with aging.
The median age of brain tumor diagnosis is around 60 years old. But certain types like medulloblastoma are more prevalent in children.
Hormones
Hormonal activity also seems to play a role in some brain tumor subtypes. Key associations include:
- Menstrual cycles – Meningiomas grow faster in women during high progesterone parts of the cycle.
- Pregnancy – Meningioma and glioma rates are lower in women who have been pregnant.
- Breast cancer – Medroxyprogesterone treatment may raise meningioma risk.
- Androgens – Androgen deprivation therapy for prostate cancer is linked to meningioma development.
This indicates hormones like progesterone, estrogen, testosterone, and related therapies can potentially influence brain tumor formation and growth patterns. The exact mechanisms are still being researched.
Conclusion
In conclusion, the development of brain tumors is a complex process that involves multiple contributing factors. Key among these are genetic mutations, radiation exposure, head injuries/infections, environmental exposures, lifestyle habits, age, and hormones. In most cases, no single cause can be pinpointed. Rather, individuals may have varying combinations of risks that collectively lead to abnormal brain cell growths over time. Understanding the predominant reasons for brain tumors allows medical professionals to better assess individual risk profiles, personalize monitoring and prevention, and improve brain tumor diagnosis and treatment.
