GFAP and central nervous system cancer: Immunohistochemical analysis is very useful in differentiating the various types gliomas as well as their subtypes.[15] The most crucial marker for detection of glial differentiation is GFAP.[15,16] Virtually all gliomas secret S-100 protein, making it a sensitive marker for these malignancies.[15] Nevertheless, S-100 secretion is a relatively nonspecific glioma marker because a variety tumors secrete it.[15] OLIG2 does not permit for obvious differentiation between oligodendrogliomas and diffuse or pilocytic astrocytomas.