Therefore, gene sequencing analysis for IDH1 R132H-negative astrocytic tumors is reserved for grade 4 astrocytoma patients of <55 years of age and not necessary in WHO grade 4 tumors if the age of the patient is >55 years. The frequency of IDH1 mutation in grade 2 astrocytomas varied from 42.5% to 100% in various studies, but in the present study, it was 57.9% (Table 2) [3,4,12-14]. Here, IDH1 is linked to astrocytoma (excluding glioblastoma).