What is Brain Cancer?

Brain cancers are abnormal growths of tissue found inside the skull. The brain is a soft spongy mass of nerve cells and supporting tissue. It controls every physiological system in the body and is responsible for our thoughts, language and emotions. In the brain, any abnormal growth puts pressure on sensitive structures and may impair their function. Tumors that occur in the brain may be either benign (non-cancerous), or malignant (cancerous). Benign brain tumors do not contain cancer cells or invade other tissue, but they can cause pressure in areas of the brain and cause symptoms. Malignant tumors that start in any tissue of the brain are classified as primary brain cancer or brain cancer. Primary brain cancer rarely metastasizes (spreads) to other parts of the body. Cancer that starts in another part of the body and metastasizes to the brain is classified as secondary brain cancer or metastatic brain cancer. Primary brain cancer and secondary brain cancer are usually treated differently.

There are two types of brain tumors: primary brain tumors that originate in the brain and metastatic (secondary) brain tumors that originate from cancer cells that have migrated from other parts of the body. Doctors classify primary brain tumors according to the type of brain cells they develop from, the appearance of individual cells under the microscope, their location in the brain, or a combination of these factors. More than half of adult brain tumors are gliomas, which means they arise in the tissue in the brain known as glial tissue. Examples include astrocytomas, which start in brain cells called astrocytes, and glioblastomas, which are particularly aggressive forms of astrocytomas.

Like any cancer, brain cancer gets its start when cells start dividing abnormally and uncontrollably, forming growths known as tumors. But not all tumors are cancerous. Some are benign, meaning that they are caused by overgrowth of normal cells. Benign tumors tend to grow slowly and don't spread, or metastasize, in the same way that malignant tumors do. Still, benign tumors in the brain or spinal cord can pose a threat to health because they can compress and destroy adjacent vital tissue or increase pressure in the skull. Cancerous tumors in the brain typically don't spread to distant areas of the body, but they can invade other areas of the brain and the spinal cord.

Cancers that start in the brain are called primary brain cancers. Cancers that start in another part of the body and spread to the brain are called secondary brain cancers or metastatic brain cancer. These are much more common than primary brain tumors. Metastatic brain cancer most often spreads from the lung, breast, kidney, and skin (melanoma). Brain cancers are generally named after the tissue in which they arise. Majority are glima arising from glial cells in the brain. These include astrocytomas, oligodenrogliomas, ependymomas and mixed cell type gliomas. The other forms of brain cancers are meningiomas, medulloblastomas, chordomas and central nervious system lymphomas.

Brain cancers can be fast growing (high grade), such as glioblastoma multiforme or slow growing (low grade), such as pilocytic astrocytoma. Cancers from other organs can spread to the brain and are called brain metastases. Brain metastases comprise cancer cells from the original site of cancer, such as lung cancer cells and breast cancer cells.

Brain cancer is not very common, and unlike many other cancers, does not usually spread to other parts of the body. Since the brain controls learning, memory, senses (hearing, visual, smell, taste, touch), emotions, muscles, organs, and blood vessels, all cancerous brain tumors are life threatening.