ABTA primer excerpt Copyright ABTA
“Astrocytoma Grade IV
also called Glioblastoma Multiforme
“Grade IV astrocytoma,” “glioblastoma,” “glioblastoma multiforme,” and “GBM” are all names for the same tumor. Glioblastomas arise from astrocytes – star-shaped cells which form the supportive, glue-like substance of the brain. These tumors represent about 20% of all primary brain tumors and about 50% of astrocytomas. They are more common in older adults, and affect more men than women. Only nine percent of childhood brain tumors are glioblastomas.
Glioblastomas are generally found in the cerebral hemispheres of the brain, but technically can be found anywhere in the brain or spinal cord. Because the glioblastoma is capable of very rapid growth, the first symptoms are usually due to increased pressure in the brain. Headaches, seizures, memory loss, and changes in behavior are the most common presenting symptoms.
Glioblastomas commonly contain a mix of cell types. It is not unusual for the tumor to contain cystic material, calcium deposits, blood vessels, or a mixed grade of cells. Brain tumors, however, are graded based on the most malignant cell found in the tumor, and any astrocytoma that contains necrotic (dead) cells and an extensive network of blood vessels is generally a glioblastoma. The lack of uniformity from end to end of the tumor makes a glioblastoma one of the most difficult brain tumors to treat. While one cell type may be responsive to treatment, other types may be resistant.
The first step in treating a glioblastoma is surgery to remove as much tumor as possible. Radiation therapy almost always follows surgery or biopsy. There are several different forms of radiation therapy – ranging from conventional external beam radiation to stereotactic radiosurgery to conformal radiation therapy – which might be suggested. Other types of radiation therapy, such as implanted liquid radiation or monoclonal antibodies tagged with radioactive particles, may also be considered.
Chemotherapy might be given before, during or after radiation. The most commonly used drugs for adults are BCNU, CCNU, procarbazine, and temozolomide. Biodegradeable wafers containing BCNU may be placed in the cavity created by tumor removal. Other new delivery systems are under investigation. Chemotherapy might also be used in children under the age of three to delay radiation.
Antisense therapies block the messages given off by malignant cells, altering their ability to interfere with the normal growth of surrounding cells. Protease inhibitors, such as marimastat and tamoxifen, block the ability of tumor cells to make the proteins needed for tumor cell reproduction. Angiogenesis inhibitors may be capable of interupting the blood supply to a tumor, thus controlling tumor growth.
Immunotherapy is the use of the body’s own immune system to fight a tumor. There are several research studies focusing on this area of treatment, and many of the programs are open to those with a glioblastoma. Immunotoxins, such as diptheria or pseudomonas, link a toxin to an antibody and carry it to the tumor cells. Interferons are thought to inhibit tumor cell growth by stimulating the immune system; they may also be angiogenesis inhibitors. Other researchers are using gene therapies as a way of controlling tumor growth. In one method, specially-engineered genes make tumor cells more susceptible to drug therapy. In another method, gene therapy is used to stimulate the body’s natural production of immune substances. Gene therapy may also be used to restore the normal function of tumor suppressing genes within tumor cells.
Recurrent tumors can be treated with additional surgery, another form of focused radiation, chemotherapy, or any number of experimental approaches as mentioned above. “