For the <55-year age group, out of 18 cases of glioblastoma, six cases were categorized as glioblastoma, IDH1 mutant type, due to immunoreactivity for IDH1, and 12 cases were categorized as glioblastoma, NOS (not otherwise specified), due to IDH1 negativity. The gene discussed is IDH1; the disease is glioblastoma.