P16 immunohistochemistry is a sensitive and specific surrogate marker for CDKN2A homozygous deletion in gliomas

Abstract

AbstractMolecular characterization of gliomas has uncovered genomic signatures with significant impact on tumor diagnosis and prognostication.CDKN2Ais a tumor suppressor gene involved in cell cycle control. Homozygous deletion of theCDKN2A/Blocus has been implicated in both gliomagenesis and tumor progression through dysregulated cell proliferation. In histologically lower grade gliomas,CDKN2Ahomozygous deletion is associated with more aggressive clinical course and is a molecular marker of grade 4 status in the 2021 WHO diagnostic system. Despite its prognostic utility, molecular analysis forCDKN2Adeletion remains time consuming, expensive, and is not widely available. This study assessed whether semi-quantitative immunohistochemistry for expression of p16, the protein product ofCDKN2A, can serve as a sensitive and a specific marker forCDKN2Ahomozygous deletion in gliomas. P16 expression was quantified by immunohistochemistry in 100 gliomas, representing both IDH-wildtype and IDH-mutant tumors of all grades, using two independent pathologists’ scores and QuPath digital pathology analysis. MolecularCDKN2Astatus was determined using next-generation DNA sequencing, with homozygousCDKN2Adeletion detected in 48% of the tumor cohort. ClassifyingCDKN2Astatus based on p16 tumor cell expression (0–100%) demonstrated robust performance over a wide range of thresholds, with receiver operating characteristic curve area of 0.993 and 0.997 (blinded and unblinded pathologist p16 scores, respectively) and 0.969 (QuPath p16 score). Importantly, in tumors with pathologist-scored p16 equal to or less than 5%, the specificity for predictingCDKN2Ahomozygous deletion was 100%; and in tumors with p16 greater than 20%, specificity for excludingCDKN2Ahomozygous deletion was also 100%. Conversely, tumors with p16 scores of 6–20% represented gray zone with imperfect correlation toCDKN2Astatus. The findings indicate that p16 immunohistochemistry is a reliable surrogate marker ofCDKN2Ahomozygous deletion in gliomas, with recommended p16 cutoff scores of ≤ 5% for confirming and > 20% for excluding biallelicCDKN2Aloss.