HLA-E and diffuse astrocytoma: We found that HLA-E expression was significantly higher in diffuse astrocytomas than it in oligodendrogliomas (− 0.255 ± 0.762 versus − 0.636 ± 0.879, p = 0.032, t-test, Fig. 2a), while no such difference was observed between anaplastic astrocytomas and anaplastic oligodendrogliomas (p = 0.671, t-test, Fig. 2b).