Tumors that start in the brain are called primary brain tumors. Tumors that start elsewhere in the body and spread to the brain are metastatic brain tumors.
Malignant (cancerous) tumors are typically rapidly growing and aggressive. Benign tumors are typically slow- growing and less aggressive. Primary brain tumors can be malignant, intermediate (between malignant and benign), or benign. Malignant primary brain tumors are dangerous because of their tendency to invade the brain, but they rarely spread outside the brain. Metastatic brain tumors are almost always malignant.
Primary brain tumors
Primary brain tumors are typically rated by a neuropathologist on a scale of I-IV, based on the appearance of the tumor under a microscope:
- Grade IV: Highly malignant. Glioblastoma is the most common type.
- Grade III: Also malignant, but not as aggressive as grade IV.
- Grade II: Serious tumors that invade the brain. Less aggressive than grade III. Sometimes considered benign, but probably best considered as being borderline malignant.
- Grade I: Tumors that are usually slow growing, less invasive, and sometimes curable by surgery.
The type of tumor is determined by the pathologist based on the type of cell that the tumor resembles, which may also be the type of cell in which the tumor originates. The most common types of tumors and their treatments include:
- High-grade gliomas include grade IV and grade III astrocytomas, oligodendrogliomas, and oligoastrocytomas. The most common is glioblastoma (grade IV astrocytoma). The usual treatment after surgery is radiation and chemotherapy. Treatment is often in clinical trials.
- Low-grade gliomas (grade III) include astrocytomas, oligodendrogliomas, and oligoastrocytomas. Treatment after surgery may be with radiation or chemotherapy. If these tumors are not growing rapidly or causing symptoms, sometimes they will be watched without additional treatment. Treatment may be in clinical trials.
- Very low-grade tumors (grade I) are often treated only with surgery, but sometimes radiation or chemotherapy may be recommended.
- Meningiomas are usually treated with surgery. When they cannot be safely removed, or if they grow back after surgery, radiation may be recommended.
- Primary central nervous system lymphoma is typically treated with multidrug chemotherapy.
What causes primary brain tumors?
Many advances have been made in our understanding of brain tumors in recent years, especially for the more common types of malignant brain tumors. These tumors generally have several mutations (abnormalities in the DNA) most of which are present only in the tumor cells and not elsewhere in the body. These mutations tend to be in specific areas of the DNA, and the presence of mutations in the DNA in these regions allows the cells to grow and divide out of control. Much remains to be learned about the cause of these mutations and the manner in which they permit cells to grow and divide abnormally. Even more important, much remains to be learned how knowledge of the causes of these tumors can be used to devise more effective treatments.