tumors. Mini-germistocytes are found to have a very ordered arrangement of filaments throughout the cytoplasm, but may also transform into the end-state morphology of the larger gemsitocytic cells. Studies have suggested that both classic gemistocytes and mini-gemistocytes show similar genetic variation to non-gemistocytic tumor cells. Mini-germistocytes, usually found in oligodendroglial tumor cells, express gliofibrillary oligodendrocytes, or GFOCs, which are capable of transforming the mini-gemistoctyes into larger gemistocytes. Gliomas A common form of a gemistocytic tumor, the gemistocytic astrocytes, consists of gemistocytes and giant cellular sarcoma. Gemistocytic astrocytomas are considered a specific type of diffuse astrocytic tumor that can be characterized by gemistocytes, and they usually appear during acute injury; after that, they gradually shrink in size. The gemistocytic cells can occur sporadically or locally in gliomas, which leads to the biology of the tumor. Astrocytes participating in gliosis are referred to as reactive astrocytes. Gemistocytic astrocytes are assumed to be intensely active cells because the astrocytomas evolve into glioblastomas. Tritiated thymidine can be used to determine the rate of cell division and cellular origins of gemistocytic astrocytes, leading to the discovery of the relationship between tumor anaplasia and degeneration. Tumor and brain tissue can be examined using autoradiographs, showing if the gemistocytic astrocytes could be labeled by the tritiated thymidine. Because there is a very large amount of cytoplasm, the giant gemistocytic astrocytes appear to be unable to incorporate tritiated thymidine, or unable to synthesize DNA, which suggests that gemistocytic astrocyte cells leave a proliferating pool after mitosis, and change to form gemistocytes. The original morphology of gemistocytes is uncertain, but it is known that they incorporate tritiated thymidine as either fibrillary or protoplasmic astrocytes. Gemistocytes multiply at a very slow rate, and their origin is very closely related to changes within the tumor. This speculates that gemistocytes show a very low proliferative activity, which means they grow at a very slow rate, and do not copy DNA well. Normal central nervous system development involves differentiation from stem cells to progenitor cells, which can then transform into fully differentiated cells. All types of tumors are derived from either multipotent stem cells, or progenitor cells. Gene expression patterns are very likely to overlap for stem and progenitor cells and the tumors that are derived from them, but patterns are less likely to overlap for differentiated cells. Glioma grading The glioma grading system distinguishes four grades for astrocytomas and two grades for