Causes of Brain Tumors
Brain tumors are collections of cells that have lost the ability to control their own growth and replication. As these cells accumulate, they form masses that can grow within the confined space of the skull and bones of the spine. These masses can apply pressure on the brain and spinal cord and cause significant injury over time. While it’s important to know about the different types of brain tumors, it’s also important to know how they start. In this article, we’ll discuss what influences brain tumor development and the causes of brain tumors.
Risk Factors for Brain Tumors
There are several factors, including certain genetic syndromes and radiation exposure, that may increase your risk of developing a brain tumor. The most common risk factors are:
- Radiation exposure: People exposed to a type of radiation called ionizing radiation have an increased risk of developing brain tumors. The radiation used during cancer treatment and radiation exposure through radioactive materials, such as an atomic blast, can damage genetic material (DNA) in cells, leading to mutations or changes that can cause cells to grow and divide uncontrollably, eventually forming a tumor.
- Family history and genetic disorders: Patients with certain genetic disorders or a family history of brain tumors may be at increased risk for brain tumors. Table 1 below provides a list of the genetic disorders and the types of brain tumors they are associated with.
- Age: The risk of brain tumors increases with age, with most brain tumors being diagnosed in people over the age of 60. This increased risk in older people may be caused by the DNA damage that occurs as cells naturally age, chronic inflammation and weakened immune systems, and increased exposure to environmental factors.
- Exposure to certain chemicals: Exposure to some solvents or pesticides may increase the risk of developing a brain tumor. Solvents such as benzene, toluene, and xylene, which are commonly used in the chemical and petrochemical industries, have been linked to an increased risk of brain tumors. Similarly, pesticides such as organophosphates and carbamates have been linked to an increased risk of brain tumors. More research is needed to fully understand the relationship between exposure to solvents and pesticides and the risk of brain tumors.
- Infections: Certain infections, such as human papillomavirus (HPV), may increase the risk of developing a brain tumor. Also, those who have a compromised immune system and have been previously infected by Epstein-Barr virus (EBV) have an increased risk of developing cancer. For example, people with HIV who have had a previous Epstein-Barr virus infection are more likely to get primary central nervous system lymphoma (PCNSL). Although primary central nervous system lymphoma is not technically a brain tumor, it originates in the brain.
| Neurofibromatosis type I | Optic glioma, astrocytoma, neurofibroma |
| Neurofibromatosis type II | Acoustic neuroma, meningioma, ependymoma, astrocytoma |
| Tuberous sclerosis | Subependymal giant cell astrocytoma |
| Von Hippel-Lindau | Hemangioblastoma |
| Turcot syndrome | Glioblastoma multiforme, anaplastic astrocytoma, medulloblastoma, pineoblastoma |
| Li-Fraumeni | Astrocytoma |
| Cowden | Meningioma |
What Causes Tumors in the Brain?
Secondary Brain Tumors
The most common brain tumors, accounting for more than 50% of all brain tumors, are called secondary brain tumors. Secondary tumors occur when cancer that starts in another part of the body metastasizes, or spreads, to the brain. When this metastasis happens, there may be one or several secondary tumors found within the brain.
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Figure 1: Multiple metastatic tumors (metastases) within the brain.
The most common secondary cancer causing brain tumors in adults first originates in the lungs. Other common cancers that spread to the brain include melanoma, breast, colorectal, and renal cancers. Cancers of the esophagus and throat, prostate, and non-melanoma skin cancers rarely ever spread to the brain.
Children can also develop brain metastases; however, the brain tumor types in children are different than those in adults. Sarcomas (cancers of connective tissue), germ cell tumors, and neuroblastomas are the most common sources for secondary brain tumors in children. Neuroblastoma is a tumor that can arise from any immature nerve in the body. Germ cell tumor is a tumor that originates from a type of cell most often found within the reproductive organs.
Primary Brain Tumors
Primary brain tumors are the most common cause of cancer in children (0-14 years old). There are many different types of brain tumors that affect children and teenagers, and these tumors may have an inherited genetic component influencing their development. Medulloblastoma, which is a type of cerebellar tumor, is the most common primary brain tumor in children. Craniopharyngiomas also occur in children and develop near the pituitary gland, affecting hormones and a child’s growth. Other primary brain tumors found in children include astrocytomas, brainstem gliomas, and oligodendrogliomas.
Some brain tumors affect adults more than children, while others affect men more than women, and vice versa. For example, meningiomas, or tumors of the protective covering of the brain, occur twice as often in women compared with men, and medulloblastomas affect boys approximately 1.5 times more often than girls.
Inherited Genetic Syndromes
As previously mentioned, some brain tumors are caused by inherited genetic mutations. For example, neurofibromatosis type 2 (NF2) is a genetic condition that can increase the risk of developing brain tumors like acoustic neuromas, also known as vestibular schwannomas. Besides NF2, several other genetic syndromes may increase risk of developing a brain tumor, although these conditions are responsible for only about 1% to 5% of all brain tumors. Refer to Table 1 for the most common genetic conditions known to cause brain tumors.
Key Takeaways
- Brain tumors form when cells that have lost the ability to control their own growth and replication accumulate and form masses that grow within and around the brain.
- Several factors increase the risk of developing a brain tumor, including exposure to radiation or certain chemicals, age, family history and genetic disorders, and infections.
- Secondary tumors, which occur when cancer that starts in another part of the body spreads to the brain, are the cause of more than 50% of all brain tumors.
- Although children and young adults can develop brain tumors, more occur in older adults over the age of 60.
- Genetic factors may increase risk of developing a brain tumor, although these conditions cause only about 1% to 5% of all brain tumors.
