What Are the Various Types and Grades of Brain Cancer?
Primary brain tumors
The brain is made up of many different types of cells and tumors that arise from a brain cell type are termed primary brain tumors. The answer to the question "How common is a primary brain tumor?" is that this type of tumor is uncommon (about 12 per every 100,000 people per year).
- Cancers occur when one type of cell transforms and loses its normal characteristics. Once transformed, the cells grow and multiply in abnormal ways.
- As these abnormal cells grow, they become a mass of cells, or tumor.
- Brain tumors that result from this transformation and abnormal growth of brain cells are called primary brain tumors because they originate in the brain. Brain tumors occur in both pediatric and adult patient populations.
- The most common primary brain tumors are gliomas, meningiomas, pituitary adenomas, vestibular schwannomas, primary CNS lymphomas, and primitive neuroectodermal tumors (medulloblastomas). The term glioma is an expansive one since it includes numerous subtypes, including astrocytomas, oligodendrogliomas, ependymomas, and choroid plexus papillomas.
- These primary tumors are named after the part of the brain or the type of brain cell from which they arise.
Brain tumors vary in their growth rate and ability to cause symptoms. The cells in fast growing, aggressive tumors usually appear abnormal microscopically. The National Cancer Institute (NCI) uses a grading system to classify tumors. The NCI lists the following grades:
- Grade I: The tissue is benign. The cells look nearly like normal brain cells, and cell growth is slow.
- Grade II: The tissue is malignant. The cells look less like normal cells than do the cells in a grade I tumor.
- Grade III: The malignant tissue has cells that look very different from normal cells. The abnormal cells are actively growing. These abnormal-appearing cells are termed anaplastic.
- Grade IV: The malignant tissue has cells that look most abnormal and tend to grow very fast (aggressive).
Per the Central Brain Tumor Registry of the United States estimates in 2016, approximately 77,000 brain tumors will have been diagnosed in the U.S. About 25,000 will have been malignant, and about 52,800 benign (with about 22,000 cases being diagnosed as meningioma, the most common form of brain tumor, and usually a benign type). Glioma is the most common type of malignant brain tumor, with at least half being grade IV or glioblastomas, the most aggressive type of malignant brain tumor or brain cancer. This registry is being updated, so only 2012 estimated data is available at this time.
Metastatic Brain Tumors
Metastatic brain tumors are made of cancerous cells that spread through the bloodstream from a tumor located elsewhere in the body. The most common cancers that spread to the brain are those arising from cancers that originate in the lung, breast, and kidney as well as malignant melanoma, a skin cancer. The cells spread to the brain from another tumor in a process called metastasis. The process metastasis occurs when cancer cells leave the primary cancer tissue and enter either the lymphatic system to reach the lymph nodes and possible later the bloodstream or through the bloodstream directly. These cancer cells eventually reach the brain tissue through the bloodstream where they develop into metastatic tumors.
Metastatic brain tumors are the most common type of tumor found in the brain and are much more common than primary brain tumors. Metastatic tumors are usually named after the type of tissue from which the original cancer cells arose (for example, metastatic lung or metastatic breast cancer). Brain blood flow usually determines where the metastatic cancer cells will lodge in the brain; about 85% locate in the cerebrum (the largest portion of the brain, located in the upper part of the skull cavity). Unfortunately, the majority of metastatic brain tumors spread diffusely within the brain and are found at least half the time at more than one site in the brain tissue, appearing as multiple masses on the diagnostic scan.
Fifteen percent of all cancers (except for non-melanoma skin cancer, and carcinoma in situ of the cervix) will be complicated by brain metastases.