Hemizygous deletion of CDKN2A/B with p16 immuno-negative and methylthioadenosine phosphorylase retention predicts poor prognosis in IDH-mutant adult glioma

Homozygous deletion of the tumor suppression genes cyclin-dependent kinase inhibitor 2A/B (CDKN2A/B) is a strong adverse prognostic factor in IDH-mutant gliomas, particularly astrocytoma. However, the impact of hemizygous deletion of CDKN2A/B is unknown. Furthermore, the influence of CDKN2A/B status in IDH-mutant and 1p/19q-codeleted oligodendroglioma remains controversial. We examined the impact of CDKN2A/B status classification, including hemizygous deletions, on the prognosis of IDH-mutant gliomas. We enrolled 101 adults with IDH-mutant glioma between December 2002 and November 2021. CDKN2A/B deletion was evaluated with multiplex ligation-dependent probe amplification (MLPA). Immunohistochemical analysis of p16/MTAP and promoter methylation analysis with methylation-specific MLPA was performed for cases with CDKN2A/B deletion. Kaplan−Meier plots and Cox proportion hazards model analyses were performed to evaluate the impact on overall (OS) and progression-free survival. Of 101 cases, 12 and 4 were classified as hemizygous and homozygous deletion, respectively. Immunohistochemistry revealed p16-negative and MTAP retention in cases with hemizygous deletion, whereas homozygous deletions had p16-negative and MTAP loss. In astrocytoma, OS was shorter in the order of homozygous deletion, hemizygous deletion, and copy-neutral groups (median OS: 38.5, 59.5, and 93.1 months, respectively). Multivariate analysis revealed hazard ratios of 9.30 (p=0.0191) and 2.44 (p=0.0943) for homozygous and hemizygous deletions, respectively. CDKN2A/B hemizygous deletions exerted a negative impact on OS in astrocytoma. Immunohistochemistry of p16/MTAP can be utilized to validate hemizygous or homozygous deletions in combination with conventional molecular diagnosis.