Tumors 101

Tumors 101

Primary tumors

These tumors begin in the brain and tend to stay there. They account for about one-fourth of brain tumors and affect people of all ages. About 63 percent of primary tumors are benign* (not cancerous), but they can still cause pain and threaten life and brain function if not treated or removed. The most common primary cancerous tumors are gliomas, which occur in the supportive tissue of the brain. They can be irregularly shaped as they infiltrate surrounding tissue, and this can make them challenging to treat. Glioblastoma and anaplastic astrocytoma are the most aggressive and life threatening gliomas.

* American Brain Tumor Association

Metastatic tumors

These tumors come from cancer elsewhere in the body, such as the lungs or breasts. Cells from those cancers travel (metastasize) to the brain and form new tumors. Metastatic tumors account for about three-fourths of brain tumors. They are more common in adults than in children. Metastatic tumors often appear in multiple places in the body, and new tumors may continue to appear as long as the original disease remains active. By definition, metastatic tumors are not benign, but not all metastatic tumors require aggressive treatment.


These are damaged areas that can trigger abnormal nerve impulses in the brain and cause the seizures, fits, and loss of consciousness common to epilepsy and other brain abnormalities. Brain lesions can take many forms, including tumors, scar tissue, brain injury, infections, abnormal blood vessels, hemorrhage, birth defects, and others.

Brain tumor grades

The tumor grade is a description of a tumor based on how abnormal the tumor cells and tumor tissue look under a microscope. It is an indicator of how quickly the tumor is likely to grow and spread and may be one factor doctors consider when planning treatment for a patient.

Doctors assign grades to brain tumors, ranging from Grade I (least serious) to Grade IV (most serious).

  • Grade I: The tissue is benign (not cancerous). The cells look nearly like normal brain cells, and they grow slowly.
  • Grade II: The tissue is malignant (cancerous). 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 (anaplastic).
  • Grade IV: The malignant tissue has cells that look most abnormal and tend to grow quickly.

From the National Cancer Institute

Types of brain tumors

Parts of the Brain
The National Cancer Institute lists the most common types of brain tumors. Among adults, the most common types are:

  • Astrocytoma.  The tumor arises from star-shaped glial cells called astrocytes. It can be any grade. In adults, an astrocytoma most often arises in the cerebrum. Grade I or II astrocytoma may be called a low-grade glioma. Grade III astrocytoma is sometimes called a high-grade or an anaplastic astrocytoma. Grade IV astrocytoma may be called a glioblastoma or malignant astrocytic glioma.
  • Meningioma.  The tumor arises in the meninges (thin layers of tissue that cover and protect the brain and spinal cord). It can be Grade I, II, or III but is usually benign (Grade I) and grows slowly.
  • Oligodendroglioma.  The tumor arises from cells that make the fatty substance that covers and protects nerves. It usually occurs in the cerebrum. It’s most common in middle-aged adults. It can be Grade II or III.

Among children, the most common types of brain tumor are:

  • Grade I or II astrocytoma.  In children, this low-grade tumor occurs anywhere in the brain. The most common astrocytoma in children, juvenile pilocytic astrocytoma, is Grade I.
  • Ependymoma.  The tumor arises from cells that line the ventricles or the central canal of the spinal cord. It is most common in children and young adults. It can be Grade I, II, or III.
  • Brain stem glioma.  The tumor occurs in the lowest part of the brain and can be low-grade or high-grade tumor. The most common type is diffuse intrinsic pontine glioma.
  • Medulloblastoma.  The tumor usually arises in the cerebellum. It is sometimes called a primitive neuroectodermal tumor. It is Grade IV.

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