EZHIP and H3K27me3 are Useful Diagnostic Markers for Germinoma and for the Germinoma Component of Germ Cell Tumors of Central Nervous System

Abstract Background Differentiating central nervous system (CNS) germinomas from other germ cell tumors (GCTs) is diagnostically challenging. EZHIP (EZH Inhibitory Protein, encoded by CXorf67) and H3K27me3 (trimethylated histone H3 at lysine 27) are widely used in diagnosing posterior fossa group A (PFA) ependymomas, their expression in germinomas remains poorly characterized. Methods We performed a clinico-pathological and immunohistochemical (IHC) analysis of 126 CNS GCT cases. Expression of EZHIP, H3K27me3, SALL-4, OCT3/4, and PLAP was evaluated in paraffin-embedded tissues. Results In GCTs of the CNS, both pure germinomas and the germinoma component in NGGCTs, EZHIP was positive in 95.1% (97/102) of cases, loss of H3K27me3 was observed in 98.0% (100/102), SALL-4 was expressed in 100% (82/82), OCT3/4 in 98.9% (96/97), and PLAP in 96.9% (94/97). In contrast, none of the non-germinomatous components of the CNS GCTs showed EZHIP positivity (0/24), while loss of H3K27me3 was found in such components in only 12.5% of the tumors. Both markers exhibited statistically significant differential expression (P< 0.01 for each). For diagnosing germinomas, EZHIP expression demonstrated a sensitivity of 95.1% and specificity of 100%, whereas H3K27me3 loss had a sensitivity of 98.0% and specificity of 87.5%. Conclusion EZHIP expression and loss of H3K27me3 staining are good markers for recognition of pure germinomas and of germinoma components in mixed germ cell tumors as such, and can be used for discriminating those from non-germinomatous components of the CNS GCTs.