What is Cancer
Cancer develops when the cells begin to grow uncontrollably. Ordinarily, cell growth is tightly controlled. In response to our body’s needs, cells grow, divide, forming, replacing and repairing new tissues as needed. In fact, most cells have a typical life span in which they grow, mature, and with time die and are replaced with new cells. This cycle of division, growth, maturation and death is strictly regulated. This is especially true of the brain, where most cell growth halts early in life. Tumors form when this orderly process of cell growth and replacement becomes disordered. In some cases, more cells are made than the body needs. In others, cells do not die when they should. Typically, these cancerous cells do not mature normally and are unable to fulfill their normal functions. Overtime, these cells can form a mass called a tumor, from the Latin word tumere, meaning “to swell”. Most cancers are named after the organ, tissue or cell type they arise from. Breast cancer, for example, arises the cells of the breast. Lymphomas arise from the immune cells of the lymphatic system. Gliomas, a common form of brain tumor, arise from a brain cell type called glial cells. Another common brain tumor, meningioma, arises from cells from a tissue called the meninges that cover the surface of the brain.
When a cancer spreads from one part of the body to another, it is said to have “metastasized”. Cancer cells from a breast tumor, for example, can spread to the brain. Such a tumor, although located in the brain, is still a breast cancer, and in this case metastatic breast cancer.
Benign vs. Malignant
Tumors fall into two main categories, benign and malignant. Benign tumors are typically formed by slow growing cells that rarely spread. Although they can press on and damage nearby normal tissue, benign tumors are much less dangerous than malignant tumors. However, they can be life-threatening if they endanger vital brain centers. Often benign tumors can be cured with surgery alone. However, overtime, some benign tumors can become malignant. Malignant brain tumors, on the other hand, are formed by cells that typically grow quickly and are capable of invading nearby tissues and spreading to other parts of the body. Their tendencies to invade and spread make these tumors much more dangerous. Malignant tumors of the brain often spread to other parts of the central nervous system. Only relatively few spread to other parts of the body.
Metastatic vs. Primary Brain Tumors
The majority of tumors found in the brain are not, in fact, brain cancers, but are cancers from other parts of the body that have spread to the brain. Cancers that have spread from another part of the body are called metastatic cancers. The word metastatic comes from the Greek word methistanai meaning “to change”. Breast cancer, lung cancer and melanoma “a skin cancer” are the most common sources of metastatic brain cancer. The treatment of these brain cancers usually focuses on treating the original or primary cancer. Brain tumors that arise from brain cells and related structures are primary brain cancers, to indicate that they are not metastatic. This website focuses on primary tumors of the brain and spinal cord, although we do have sections on the metastatic cancers as well. Except in these sections, when we talk about brain tumors, we will be talking about primary brain tumors.
Causes of Cancer
Cancers are caused by changes in our genes. Each gene contains a string of molecules that act like letters that “spell out” the instructions our cells need to assemble a specific protein. These letters are made of molecules called deoxyribonucleic acids — DNA — and the instructions they spell out are often called the “genetic code”. When our cells “read” a gene’s instructions and produce the gene’s protein or RNA — the gene is said to be ‘expressed’. How a cell grows, develops and behaves is largely controlled by which genes are expressed or “turned on” and which are not. Changes in genes, caused, for example by the loss of or substitution on one DNA latter for another can cause the cell to assemble the protein incorrectly. Sometimes the cell will not be able to make the protein at all. Sometimes the protein will not work as it should. These changes, called mutations, often cause no harm. Sometimes, they can cause the cell to die. But sometimes they can lead to cancer. Usually more than one gene needs to be affected before a cell can become cancerous. Exposure to radiation, some chemicals and other factors in the environment can cause genetic mutations. However, many mutations simply accumulate over time as we age, which is why cancer is more common in the elderly.
In general, cancer-causing mutations involve three types of genes: Oncogenes, Tumor suppressor genes, and DNA repair genes.
Causes of Brain Tumors
The cause of most brain cancers is unknown. In general, cancers are due to a combination of inherited genetic factors coupled with some exposure during life, such as exposure to a chemical, a virus or radiation. Of these, the best case has been made for exposure to high doses of radiation, such as those given as part of cancer treatment, and an increased risk of subsequent brain cancer. Exposure to some chemicals in the workplace has also been found to increase the risk of developing brain cancer. Infections may play a role as well: the virus that causes mononucleosis, the Epstein-Barr virus, has been linked to an increased risk of a form of lymphoma that affects the central nervous system, CNS lymphoma, which also is more common among individuals infected with HIV, the virus that causes AIDS. Genetics play a particularly important role in a number of brain tumors that are clearly linked to a number of inherited disorders and disorders due to chromosome damage. Genetic damage that accumulates as we age can also trigger changes in cells that lead to brain cancer. But, again, in most cases the cause for an individual patient’s brain cancer cannot be identified.