ID #1181 H3K27me3 expression and prognosis of posterior fossa ependymoma
Piti Techavichit, Chanakarn SitlaothawornAbstract
Background
Ependymoma is the third most common brain tumor; two-thirds of ependymoma occurs in the posterior fossa area. Ependymoma is divided into posterior fossa ependymoma group A (PFA) and group B (PFB), according to the expression of H3K27me3 in an immunohistochemical study. PFA had decreased expression of H3K27me3, which often occurs in younger ages, and inferior outcomes.
Objectives
To describe H3K27me3 expression, clinical course, and treatment outcome in pediatric and adult posterior fossa ependymoma.
Methods
This study was a retrospective review of posterior fossa ependymoma diagnosed at King Chulalongkorn Memorial Hospital, Bangkok, Thailand, from January 2013 to December 2022. Immunohistochemical testing for the expression of H3K27me3 was performed from the formalin-fixed paraffin-embedded (FFPE) specimens.
Results
Of the 27 patients with posterior fossa ependymoma, 55.6% (15) were male, and the median age at diagnosis was 5.9 years (IQR 2.8-25). Immunohistochemical testing identified sixteen (59.3%) and 11 (40.7%) patients as PFA and PFB. The median follow-up time was 30.3 months (IQR 17.5-48.5). PFA was statistically significant at a younger median age of diagnosis (4.3 vs. 25.9 years, p = 0.002). PFA has a higher risk of relapse than PFB (75% vs. 18.2%, p = 0.006). The 5-year disease-free survival (DFS) in PFA was significantly lower compared to PFB (25.6% vs. 90.9%, p = 0.01). The overall DFS in our study was 36.9% [95% CI:14.4-59.8].
Conclusions
PFA occurs in young children and has inferior outcomes compared to PFB. Immunohistochemical staining for H3K27me3 is a compassionate and specific molecular surrogate to establish the molecular subgroup in posterior fossa ependymomas and can be used to predict prognosis and outcomes.