L1CAM and p65 as Predictive Markers of ZFTA Fusion in Ependymomas

Purpose: In the 2021 World Health Organization (WHO) classification, ependymomas were classified according to their anatomical localization and molecular features. The “RELA fusion‐positive ependymoma” group, which was the first defined molecular subtype in the previous (2016) classification, was included as “ZFTA fusion‐positive ependymoma” in the final classification. We aimed to determine ZFTA fusion‐positivity in supratentorial (ST) and posterior fossa (PF) ependymomas and to investigate the correlation with both L1CAM and p65 immunoreactivity. Methods: The study included 17 ST and 9 PF cases with Grades 1, 2, and 3 ependymomas. The presence of the ZFTA fusion was evaluated using the fluorescence in situ hybridization (FISH) technique. L1CAM and p65 antibodies were applied for immunohistochemical analysis. The immunoreactivity for L1CAM and p65 was correlated with ZFTA fusion as assessed by FISH. Prognostic significance of the same was evaluated using the Kaplan–Meier survival analysis. Results: ZFTA fusion‐positivity was detected in 7 of 12 (58%) ST‐localized Grade 3 ependymoma cases; however, it was not observed in PF‐localized cases or in ST‐localized Grade 1 subependymoma (SE) and Grade 2 ependymoma cases. Six of the seven ZFTA fusion‐positive cases exhibited clear cell morphology. All ZFTA fusion‐positive cases showed L1CAM immunohistochemical positivity, and six of them also demonstrated nuclear p65 positivity. Moreover, we identified a new FISH pattern, which we termed the “short break‐apart.” Conclusion: Together, these data indicate a strong correlation between FISH and immunohistochemistry results. However, a more reliable assessment on this matter could be accomplished through a multicentric study involving a larger number of cases.