CDK4, CDK6, cyclin D1, p16(INK4a) and EGFR expression in glioblastoma with a primitive neuronal component

Glioblastoma with primitive neuroectodermal tumor-like component (GBM-PNET) is a rare variant of glioblastoma, which was renamed as glioblastoma with a primitive neuronal component (GBM-PN) in new WHO classification of tumours of the central nervous system in 2016. There are few publications on the investigation of GBM-PN. In this study, PCR mRNA arrays on 6 cases of conventional GBM and 10 cases of GBM-PN showed high mRNA level of CDK4 in GBM-PN and low mRNA level of EGFR in GBM-PN. Immunohistochemical stains on tissue microarrays with 28 cases of conventional GBM and 13 cases of GBM-PN demonstrated that CDK4 was selectively expressed in the primitive neuronal component of all GBM-PN cases while EGFR was positive in conventional GBM and glial component of GBM-PN, but was negative in the primitive neuronal component of all GBM-PN cases. Immunohistochemical stains with antibodies against proteins that interact with CDK4 in cell cycle regulation, such as CDK6, cyclin D1 and p16(INK4a), were performed on these GBM-PN and GBM cases. CDK6 was patchily positive in rare cases of GBM-PN and cyclin D1 was negative in GBM-PN cases. p16(INK4a) is traditionally known as an inhibitor of CDK4 and CDK6. p16(INK4a) might not be the inhibitor of CDK4 in GBM-PN cases because seven GBM-PN cases were positive for both CDK4 and p16(INK4a). It indicates that CDK4 and p16(INK4a) might play a crucial role in GBM-PN pathogenesis. Since CDK4 and EGFR are highly expressed in the primitive neuronal component and in the glial component of GBM-PN respectively, the combination of CDK4/6 inhibitor and targeted therapy against EGFR might be potential effective therapeutic regimen for GBM-PN. CDK4 and EGFR immuohistochemical stain patterns make the diagnosis of GBM-PN much easier.