Gliomas are a class of tumor that develops from glial (neuroepithelial or support) cells, which compose the supportive tissue of the brain. Cells called astrocytes, ependymal and oligodendroglia are all examples of glial cells. Gliomas comprise nearly one-half of primary brain tumors and one-fifth of all primary spinal cord tumors. Low-grade gliomas are slow growing and are assigned either a I or II grade. The grade of a tumor depends on how abnormal the cancer cells look under a microscope and how quickly the tumor is likely to grow and spread. Grade I tumors resemble normal cells and tend to grow and multiply slowly. Grade I tumors are generally considered the least aggressive in behavior. Conversely, the cells of Grade III or Grade IV tumors do not look like normal cells of the same type.
High-grade (malignant) gliomas grow much more quickly and are assigned either a III (anaplastic) or IV (glioblastoma multiforme) grade. Combined, grade III and IV gliomas represent about 40 percent of all primary brain tumors in patients 40-49 years of age, and 60 percent in patients over 60. In most clinical series, grade III tumors comprise approximately 10 percent and grade IV 90 percent of the total number of high-grade, malignant primary brain tumors.
Malignant gliomas are one of the most devastating tumors that can affect any individual. Nevertheless, this past decade, major advances in the fields of molecular biology and cellular biology, as well as genomics, have begun to improve our understanding of malignant gliomas. Grade IV gliomas, often referred to as glioblastoma multiforme or GBM, possess multiple genetic and chromosomal abnormalities that cause these tumors to grow rapidly. These tumors are unique in their ability to multiply uncontrollably, and aggressively invade, infiltrate and destroy neighboring areas of the brain. However, it is very rare for such tumors to metastasize (spread) outside the central nervous system. As a GBM progresses, portions of the tumor often outgrow the immediate blood supply and die. In contrast, outer regions of the tumor readily supply the growth of new blood vessels (angiogenesis), enabling continued rapid growth of the GBM.