A brain tumor is simply a mass caused by abnormal cell growth on or near the brain. Brain tumors can vary widely in growth rate, size, and location, and can be both noncancerous and cancerous. Tumors can also differ in origin, either originating in the brain, called a primary brain tumor, or elsewhere in the body, called a metastatic brain tumor.

Primary tumors form on the brain when normal cells have an erroneous mutation in their DNA which provides them with the means to grow and divide at an increased rate while also allowing them to survive when other, natural cells would die. The result is a mass of unnatural cells which form the tumor. Primary tumors are relatively rare and not always cancerous.

Secondary, or metastatic tumors, occur when cancer forms in another part of the body and spreads to the brain. These occur much more frequently than primary tumors and most often are found in people with a history of cancer.

As noted above, not all brain tumors are cancerous. Benign (non-cancerous) tumors are similar to cancer because they form through the growth of abnormal cells. However, these cells cannot spread and do not affect nearby tissue depending on their location. They are simply stagnant masses of cells. However a benign tumor on the brain can still pose a threat simply because it can compress sensitive brain matter.

Malignant tumors on the other hand are cancerous and have the ability to multiply and spread to various parts of the body. Like benign tumors, malignant tumors often form as the result of erroneous DNA, however they are not anchored to their original growth site and have the ability to travel throughout the body using the bloodstream.

Any tumor in the brain can pose serious health risks, as it affects the functions of the central nervous system and should be addressed by a physician.