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Utility of Immunohistochemistry in Subtyping Posterior Fossa Group A Ependymoma: A Retrospective Study
Abhishek Chowdhury1,2, Shilpa Rao2, Arimappamagan Arivazhagan3
1Department of Pathology, Gouri Devi Institute of Medical Sciences and Hospital, Durgapur, West Bengal, India.
Introduction:
Posterior fossa ependymomas are classified into posterior fossa group A (PFA-EPN) and posterior fossa group B ependymomas. PFA-EPN shows immunohistochemical loss of H3 p.K27me3 expression. Molecular subgroup 1 (PFA-1) and 2 (PFA-2), encompass nine subtypes (PFA 1a-1f and 2a-2c). OTX2 and H3 p.K27M immunopositivity is noted in PFA-2c and 1f, respectively, with potential prognostic implications.
Aim:
To assess the frequency of OTX2 and H3 p.K27M immunopositivity in PFA-EPN.
Materials And Methods:
This retrospective study included PFA-EPN diagnosed at our institute from 2016 to 2022, based on immunohistochemical loss of expression of H3p.K27me3. Immunohistochemistry for OTX2 and H3 p.K27M was carried out on them.
Results:
A total of 42 cases of PFA-EPN were encountered, ranging 10 months to 23 years, with a median of 4 years. OTX2 immunopositivity was seen in four cases (9.5%) and H3 p.K27M positivity in two cases (4.8%). Follow-up data were available partially and showed variable survival.
Conclusion:
PFA-EPN can be segregated into OTX2 and H3 p.K27M immuno-positive tumors. Because of low frequency and few studies, long-term survival data are limited. Assessment of frequency of OTX2 and H3 p.K27M immunopositivity and their segregation into subsets with prognostic significance can help in diagnostics in routine laboratory settings. This can also potentiate open new therapeutic avenues in PFA-EPN.
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