IDH2 and olfactory neuroblastoma: We performed an immunohistochemical validation of this marker combination (Fig. 3C) and observed strong staining of KRT18 in all cases of the NEC-like IDH2 and NEC-like SMARCA4/ARID1A class, variable staining intensity in the ACC class and no staining in all investigated olfactory neuroblastomas and most squamous cell carcinomas (Fig. 3D).