Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes. These gene changes can be inherited from a parent, but more often they happen during a person’s lifetime.

Primary brain tumors originate in the brain itself or in tissues close to it, such as in the brain-covering membranes (meninges), cranial nerves, pituitary gland or pineal gland. Primary brain tumors begin when normal cells develop changes (mutations) in their DNA. A cell’s DNA contains the instructions that tell a cell what to do. The mutations tell the cells to grow and divide rapidly and to continue living when healthy cells would die. The result is a mass of abnormal cells, which forms a tumor.

In adults, primary brain tumors are much less common than are secondary brain tumors, in which cancer begins elsewhere and spreads to the brain. Brain tumors can be caused by a variety of factors, including genetics, environmental exposures, and certain medical conditions. However, in many cases, the exact cause of a brain tumor is not known.

Risk factors include:

Exposure to radiation and certain chemicals: People who have been exposed to a type of radiation called ionizing radiation have an increased risk of brain tumor. Examples of ionizing radiation include radiation therapy used to treat cancer and radiation exposure caused by atomic bombs. Brain tumors, such as gliomas, may be caused by exposure to such harmful chemicals or radiation.

Cancers that spread from other parts of the body: Through a process called metastasis, cancer cells that have broken off from the primary tumor site may travel through the bloodstream or the lymphatic system to reach the brain. The most common types of cancer that spread to the brain include lung cancer, breast cancer, melanoma, and kidney cancer. These primary tumors have the ability to metastasize to the brain due to the blood-brain barrier which allows for the cancer cells to cross into the brain tissue to cause brain tumors.

Family history of brain tumors: Certain genetic conditions can predispose a person to overproduction of certain cells. A small portion of brain tumors occur in people with a family history of brain tumors or a family history of genetic syndromes that increase the risk of brain tumors. For example, some brain tumors such as meningiomas and schwannomas, are thought to be related to gene mutations that are inherited from a person’s parents.

HIV/AIDS: People with HIV or AIDS have an increased risk of developing a type of brain tumour called a CNS lymphoma. The reason for this is not completely understood, but it is likely to be due to the weakening of the immune system, particularly in advanced/late stages of HIV/AIDS. In almost all cases of lymphoma, a virus called the Epstein-Barr virus is found. However, anti-retroviral medicines, which help to slow down the progression of HIV, also lower the risk of developing neurological effects of HIV/AIDS, such as CNS lymphomas.

Certain medical conditions: such as neurofibromatosis and Li-Fraumeni syndrome, can also increase a person’s risk of developing a brain tumor.

Being overweight or obese: Around 2% of brain tumours are thought to be caused by obesity. There is now evidence that women who are overweight or obese have an increased risk of developing a type of brain tumour called a meningioma. There is also some evidence that children born weighing more than 4kg (8lbs 13oz) are at a higher risk of developing types of brain tumours called astrocytoma or embryonal tumours.

Other factors: Other factors, for which some studies have shown an increase in the risk of developing certain types of brain tumour, include:

• age (people aged 75 years and over)
• gender (slightly more females develop brain tumours than men)
• previous cancer (childhood brain and other solid tumours, non-Hodgkin lymphoma, leukaemia, melanoma, thyroid or prostate cancers).

It’s important to note that most people with brain tumors do not have any known risk factors, and it is not always possible to determine the cause of a brain tumor.