We did find faint TTF-1 expression in a single case of astrocytoma, IDH-mutant, CNS WHO grade 4 without primitive component, indicating a high sensitivity but not specificity for the TTF-1 EP229 clone for primitive neuronal component, or perhaps the detection of a tumour that is in the process of transitioning to ASTRO PNC. The gene discussed is TTF1; the disease is astrocytoma (excluding glioblastoma).