SOX10 and Olig2 as negative markers for the diagnosis of ependymomas: An immunohistochemical study of 98 glial tumors.

SOX10 belongs to the family of transcription factors essential for the development of neural crest, peripheral nervous system and melanocytes. It is presently used in histopathology as a marker of melanocytic differentiation. SOX10 is expressed in normal brain tissue in oligodendrocytes, but the information about SOX10 expression in primary tumors of the central nervous system is quite limited. In this study, we examined the expression of SOX10 and Olig2 by immunohistochemistry in a series of 98 glial tumors and explored their specificity and sensitivity for differential diagnosis of ependymal vs non-ependymal tumors. In addition, we examined the expression of EMA and CD99 in ependymal tumors. SOX10 and Olig2 staining were scored as negative if no positive cells or only a few positive cells (typically up to 1-3%) were found. In all other instances, SOX10 or Olig2 staining was scored as positive. Out of 44 examined ependymal tumors none was found to express SOX10 and 7 specimens showed only a few SOX10-positive cells that likely corresponded to entrapped non-neoplastic oligodendrocytes. In contrast, non-ependymal tumors expressed SOX10 in 26/54 (48%) specimens. Olig2 was positive in 5 out of 44 ependymomas (11%) and 50 out of 54 (93%) non-ependymal tumors (astrocytomas and oligodendrogliomas). EMA and CD99 expression was found in 33/44 (75%) and 11/44 (25%) of ependymomas, respectively. SOX10-positivity rules out the diagnosis of ependymoma among other glial tumors with high confidence.