PATH-03. DIFFERENCES IN CLINICAL COURSE OF GROUP-A AND GROUP-B POSTERIOR FOSSA EPENDYMOMA (PFA, PFB) AS DEFINED BY H3K27ME3 IMMUNOHISTOCHEMICAL ANALYSIS

Abstract

Abstract PURPOSE Posterior fossa ependymoma is classified as PFA and PFB based on underlying genetic/mutational characteristics, and PFA is reported to have poor prognosis compared to PFB. Recently, immunohistochemical findings of negative H3K27me3 have been reported to suggest PFA and attracted the attention as a surrogate marker. We classified our cases into PFA and PFB guided by immunohistochemical staining results of H3K27me3 and examined their clinical course. MATERIALS AND METHODS Between 1999 and 2018, 17 cases of posterior fossa ependymoma were treated at our institute. Negative immunostaining for H3K27me3 was classified as PFA, and positive as PFB. We evaluated age, gender, pathological diagnosis, progression free survival (PFS) and overall survival (OS) in both groups. RESULTS Nine cases were classified as PFA and eight as PFB. The median age of the PFA group was 4 years-old, 4 males, 5 females, pathological diagnosis was ependymoma in 5, and anaplastic ependymoma in 4 cases. The median follow-up period was 50 months, recurrence was confirmed in 5 cases (56%), PFS was 27.6 months. Three of the 5 patients who relapsed died (33%), and the OS was 50 months. The median age of the PFB group was 50 years, 4 males and 4 females, the pathological diagnosis was ependymoma in 6, and the anaplastic ependymoma in 2 cases. The median follow-up period was 111 months, recurrence was observed in 2 cases (25%), PFS was 98 months and all patients were alive during the period of this research. CONCLUSION Immunohistochemical results of H3K27me3 correlated with prognosis, implying the possibility of it being a surrogate marker of posterior fossa ependymoma.