Fig. 4.

Immunohistochemical features in typical lower grade infiltrating gliomas. Oligodendrogliomas (a) are immunoreactive for IDH1 R132H (b) unless they have a less common non-canonical mutation, in which case sequencing of IDH1 and IDH2 is required; they lack ATRX mutations and therefore retain nuclear reactivity of ATRX protein in tumor cell nuclei (c), and p53 immunoreactivity is generally low (d), except in anaplastic cases. Astrocytomas with IDH mutation (e-f) and ATRX mutations almost always show loss of ATRX staining in tumor nuclei, while endothelial cells (black arrow) and entrapped normal cells are positive, providing an internal positive control (g). TP53 mutations are associated with increased staining in tumor cell nuclei (h)