ATRX Immunohistochemistry, Rationale and Clinical Significance:
The majority of grade II and III infiltrating gliomas and those glioblastomas derived from them have mutations of IDH1 codon 132 or IDH2 codon 172 7. Mutations of IDH1 or IDH2 are only very rarely found in other tumor types 8. An antibody to the most common mutant form of IDH1 (R132H), accounting for the vast majority of mutations detected, has recently been developed 9-11. Positive immunohistochemistry in this setting argues strongly for the diagnosis of infiltrating glioma 12, 13.
While IDH testing provides important information for the classification of infiltrating gliomas, additional subclassification has become the standard of care, since this provides additional important prognostic and predictive information6 and is incorporated into the 2016 update of the World Health Organization classification of tumors of the nervous system14.
Two large groups of IDH-mutant infiltrating gliomas are evident, and correspond roughly to the morphologic categories of oligodendroglioma (1p/19q codeleted) and astrocytoma (1p/19q nondeleted).
1p/19q codeletion is associated with oligodendroglial appearance, longer survival and better response to therapy, but its evaluation requires copy number analysis (often performed by fluorescence in situ hybridization), which is expensive and time consuming. Hence, in order to improve turnaround time, many laboratories rely on immunohistochemical stains for ATRX 15 and/or p53, which are associated with astrocytic differentiation.
Submit a formalin-fixed, paraffin embedded tissue block
Formalin-fixed, paraffin embedded (FFPE) tissue block
Tissue section mounted on a charged, unstained slide
Immunohistochemical staining and microscopic examination
If requested, an interpretive report will be provided