IDH1 and cancer: However, it should be stressed here that IDH1mt glioblastoma cells are extremely difficult to grow in vitro, and thus cells overexpressing IDH1mt are used that do not reflect the activity of naturally occurring IDH1mt cancer cells, especially because the 1:1 stoichiometry of heterodimers of wild-type and mutated IDH1 enzymes cannot be reliably replicated with overexpression systems.