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to the cell may activate a growth factor. Human epidural growth factor is amplified in 50% of the high-grade astrocytomas. Growth factor then recruits several proteins, which activates the ras intercellular protein. This eventually leads to translocation of proteins to the nuclear membrane that then binds to the DNA and causes a change in gene expression. This entire process was the result of stimulation of oncogenes. The body has the inherent ability to correct any DNA abnormalities. However, in tumors there is also a defect in the small p53 protein, which is a tumor suppressor gene. This tumor suppressor gene decreases cellular proliferation. It is the most commonly mutated gene in human cancers. Once the tumor continues to grow it must get through multiple barriers set up by the normal tissue. Brain tumors rarely metastasize outside the brain but do invade normal brain regions. This invasion requires the tumor cells to adhere to the tissue. This is then followed by proteases, which degraded the tissue, followed by tumor cells invading the space. In order for this to take place the tumor cells must also make their own blood vessels.
BRAIN TUMOR DIAGNOSIS
Despite the connotation of a brain tumor being ominous, some patients can be effectively cured. Other tumors can be slowed down while others may only be able to be reduced in size or even just biopsied. It is important when investigating brain tumors that the doctor makes sure that the mass is not something else such as a blood clot. If trauma has been involved a CT scan without contrast, followed by the possible use of contrast is the best first test. An MRI with and without contrast usually follows this. The MRI allows identification of the mass in multiple planes. The MRI can then be used by the neurosurgeon to plan intervention. Furthermore, the MRI can give multiple views into areas that are not readily viewed with a CT scan. MRI is best for seeing into the posterior fossa, along the cranial nerves and along the skull base. The use of contrast can help distinguish between tumors, infection and sometimes even stroke. Sometimes with an MRI there is a good idea of what the mass is, however, one must remember that the MRI is only a single snapshot in time.
TREATMENT OPTIONS
Once a mass has been identified the brain tumor team must be assembled. The team consists of the neurosurgeon, the oncologist and the radiation oncologist. A neurosurgeon could help determine if the mass is resectable, and if not, is it a mass that should be biopsied. Although the exact nature of the mass cannot be ascertained without tissue, likely possibilities can be listed. The possible treatments should then be discussed with a cancer specialist called an oncologist, and even a cancer specialist specializing in radiation called, a radiation oncologist. Together this team will discuss with each other and with the patient and the patient's family, the possible treatment alternatives. Treatments can be surgery alone, surgery with radiation therapy, surgery with radiation therapy and chemotherapy or just chemotherapy or just radiation therapy. In order to give the best treatment, usually the pathologist has to have a piece of tissue in order to make the diagnosis. At times, in order to have a better idea of the pathology, prior to biopsy, other imaging modalities may be considered. These studies may be an angiogram, or even special metabolic imaging as is done with a SPECT scan, PET scan or magnetic resonance spectroscopy. A recent advance, which helps dramatically with resection, is a functional MRI. This can be integrated with a special MRI, which is then placed into (Continued on page 40)
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