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

Abstract

Molecular characterization of gliomas has uncovered genomic signatures with significant impact on tumor diagnosis and prognostication. CDKN2A is a tumor suppressor gene involved in cell cycle control. Homozygous deletion of the CDKN2A/B locus has been implicated in both gliomagenesis and tumor progression through dysregulated cell proliferation. In histologically lower grade gliomas, CDKN2A homozygous 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 for CDKN2A deletion remains time consuming, expensive, and is not widely available. This study assessed whether semi-quantitative immunohistochemistry for expression of p16, the protein product of CDKN2A, can serve as a sensitive and a specific marker for CDKN2A homozygous 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. Molecular CDKN2A status was determined using next-generation DNA sequencing, with homozygous CDKN2A deletion detected in 48% of the tumor cohort. Classifying CDKN2A status 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 predicting CDKN2A homozygous deletion was 100%; and in tumors with p16 greater than 20%, specificity for excluding CDKN2A homozygous deletion was also 100%. Conversely, tumors with p16 scores of 6–20% represented gray zone with imperfect correlation to CDKN2A status. The findings indicate that p16 immunohistochemistry is a reliable surrogate marker of CDKN2A homozygous deletion in gliomas, with recommended p16 cutoff scores of ≤ 5% for confirming and > 20% for excluding biallelic CDKN2A loss.

CDKN2A/B deletion in IDH-mutant astrocytomas: An evaluation by Fluorescence in-situ hybridization

“…Similarly, loss of expression for p16 protein on immunohistochemistry has been shown to have high sensitivity and negative predictive value with a limited speci city for detecting CDKN2A/B deletion [2,20,21]. Speci city for predicting CDKN2A/B homozygous deletion is better when < 5% p16 positive cells nuclei and excluding homozygous deletion with > 20% positive cells [22]. However, loss of p16 expression can be seen because of different molecular alterations (including point mutation, promoter hypermethylation) apart from homozygous deletion.…”

Molecular prognostication in grade 3 meningiomas and p16/MTAP immunohistochemistry for predicting CDKN2A/B status

“…Recent work has suggested p16 and MTAP immunohistochemistry as viable surrogate markers for CDKN2A/B CNV analysis for prognostication in high-grade gliomas, 15 , 35–41 and high-grade meningiomas. 12 , 13 Our results corroborate the high concordance rates between CDKN2A/B copy-number status and p16/MTAP labeling in grade 3 meningiomas.…”