Although many of the articles reviewed in the following section were written before 2021, following the WHO 2016 classification and using terms such as “primary” and “secondary” glioblastoma, we will adapt to the WHO 2021 classification and use the term “grade 4 astrocytoma” whenever the term “secondary or IDH-mutant glioblastoma” is mentioned in the literature. The gene discussed is IDH1; the disease is glioblastoma.