Brain Tumors: Primary - Introduction

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Primary Glioma Brain Tumors

About 80% of malignant primary brain tumors are known collectively as gliomas. Gliomas are not a specific type of cancer but are a term used to describe tumors that originate in glial cells. Glial cells are the building-block cells of the connective, or supportive, tissue in the central nervous system.

Gliomas are classified into four grades that reflect the degree of malignancy. Grades I and II are considered low-grade and grades III and IV are considered high-grade. Grades I and II are the slowest-growing and least malignant; grade I tumors are generally considered borderline between benign and malignant. Grade III tumors are considered malignant and grow at a moderate rate. Grade IV tumors, such as glioblastoma multiforme, are the fastest-growing and most malignant primary brain tumors.

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There are several glial cell types from which gliomas form. The names of these gliomas and their cell types are:

Astrocytomas are primary brain tumors derived from astrocytes, which are star-shaped glial cells. Astrocytomas account for about 60% of all malignant primary brain tumors. Astrocytoma tumor types by grade include:

• Grade I. Pilocytic astrocytoma is one of the most common types of glioma in children
• Grade II. Diffuse astrocytoma (also called low-grade astrocytoma) typically occurs in men and women ages 20 - 60
• Grade III. Anaplastic astrocytoma typically occurs in adults ages 30 - 60 and is more common among men than women.
• Grade IV. Glioblastoma multiforme (GBM), also called glioblastoma, accounts for about 50% of all astrocytomas and is one of the deadliest types of brain tumors. These highly malignant aggressive tumors grow rapidly. They are most common in older adults (ages 50 - 70), particularly men. Only about 10% of childhood brain tumors are glioblastomas.

Oligodendrogliomas develop from oligodendrocyte glial cells, which form the protective coatings around nerve cells. Oligodendrogliomas are classified as either low-grade (grade II) or anaplastic (grade III). Pure oligodendrogliomas, however, are rare. In most cases they occur in mixed gliomas. Oligodendrogliomas usually occur in younger and middle-aged adults.