Grading
Of numerous grading systems in use for the classification of tumor of the central nervous system, the World Health Organization (WHO) grading system is commonly used for astrocytoma. Established in 1993 in an effort to eliminate confusion regarding diagnoses, the WHO system established a four-tiered histologic grading guideline for astrocytomas that assigns a grade from 1 to 4, with 1 being the least aggressive and 4 being the most aggressive.
The WHO-grading scheme is based on the appearance of certain characteristics: atypia, mitosis, endothelial proliferation, and necrosis. These features reflect the malignant potential of the tumor in terms of invasion and growth rate. Tumors without any of these features are grade I, and those with one of these features (usually atypia) are grade II. Tumors with 2 criteria and tumors with 3 or 4 criteria are WHO grades III and IV, respectively. Thus, the low-grade group of astrocytomas are grades I and II.
Various types of astrocytomas are given these WHO grades:
| WHO Grade | Astrocytomas | Description |
|---|---|---|
| I | Pilocytic astrocytoma, pleomorphic xanthoastrocytoma, subependymal giant cell astrocytoma, and subependymoma | Consist of slow growing astrocytomas, benign, and associated with long-term survival. Individuals with very slow growing tumors where complete surgical removal by stereotactic surgery is possible may experience total remission. Even if the surgeon is not able to remove the entire tumor, it may remain inactive or be successfully treated with radiation. |
| II | Low-grade (fibrillary) astrocytoma, mixed oligoastrocytoma | Consist of relatively slow-growing astrocytomas, usually considered benign that sometimes evolve into more malignant or as highergrade tumors. They are prevalent in younger people who are often present with seizures. Median survival varies with the cell type of the tumor. Grade 2 astrocytomas are defined as being invasive gliomas, meaning that the tumor cells penetrate into the surrounding normal brain, making a surgical cure more difficult. People with oligodendrogliomas (which might share common cells of origin) have better prognoses than those with mixed oligoastrocytomas, who in turn have better prognoses than patients with (pure) low-grade astrocytomas. Other factors which influence survival include age (younger the better) and performance status (ability to perform tasks of daily living). Due to the infiltrative nature of these tumors, recurrences are relatively common. Depending on the patient, radiation or chemotherapy after surgery is an option. Individuals with grade 2 astrocytoma have a 5-year survival rate of about 34% without treatment and about 70% with radiation therapy. The median survival time is 4 years. |
| III | Anaplastic astrocytoma | Consist of anaplastic astrocytomas. It is often related to seizures, neurologic deficits, headaches, or changes in mental status. The standard initial treatment is to remove as much of the tumor as possible without worsening neurologic deficits. Radiation therapy has been shown to prolong survival and is a standard component of treatment. Individuals with grade 3 astrocytoma have a median survival time of 18 months with treatment (radiation and chemotherapy). There is no proven benefit to adjuvant chemotherapy or supplementing other treatments for this kind of tumor. Although temozolomide is effective for treating recurrent anaplastic astrocytoma, its role as an adjuvant to radiation therapy has not been fully tested. |
| IV | Glioblastoma multiforme (GBM) | Consists of Glioblastoma multiforme (GBM), which is the most common and most malignant primary brain tumor. Primary GBM grow and spread to other parts of the brain quickly; they can become very large before producing symptom, which often begin abruptly with seizures. Less than 10% form more slowly following degeneration of low-grade astrocytoma or anaplastic astrocytoma. These are called secondary GBM and are more common in younger patients (mean age 45 versus 62 years). "Surgical removal remains the mainstay of treatment, provided that unacceptable neurologic injury can be avoided. The extremely infiltrative nature of this tumor makes complete surgical removal impossible. Although radiotherapy rarely cures glioblastoma, studies show that it doubles the median survival of patients, compared to supportive care alone." The prognosis is worst for these grade 4 gliomas. Few patients survive beyond 3 years. Individuals with grade 4 astrocytoma have a median survival time of 17 weeks without treatment, 30 weeks with radiation, and 37 weeks with surgical removal of most of the tumor followed by radiation therapy. Long term survival (at least five years) falls well under 3%. |
According to the WHO data the lowest grade astrocytomas (grade I) make up only 2% of recorded astrocytomas, grade II 8%, and the higher grade anaplastic astrocytomas (grade III) 20%. The highest graded astrocytoma (grade IV GBM) is the most common primary nervous system cancer and second most frequent brain tumor after brain metastasis. Despite the low incidence of astrocytomas compared to other human cancers, mortality is significant, as the higher grades (III & IV) present high mortality rates (mainly due to late detection of the neoplasm).
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