What does the grade of a glioblastoma tumor indicate?

Tumor grading. Grading of tumors is a way of "standardizing" the type of cancer, and thereby improving consistency of treatment between treating doctors/institutions. In gliomas as in other sites, a higher grade also implies a more aggressive tumor and potentially a poorer prognosis. However, some high grade tumors can be curable, whereas low grade tumors tend to linger but not respond to treatments.
GBM. Is considered stage iv, and gliosarcoma is pathologically different but clinically identical...Short survival, no cures, and similar treatment (resection, chemo and radiotherapy). The lower grades iii= anaplastic astrocution, and i/ii astrocytoma, oligodendroglioma. Hope this helps.
Classification. The 2007 world health organization scheme is the most widely accepted approach to classifying gliomas. Malignant or high-grade gliomas are either grade iii or grade iv. Glioblastoma (gbm) is defined as grade IV in this system.