MTAP and p16 IHC as Markers for CDKN2A/B Loss in Meningiomas

Abstract

Background: Homozygous cyclin-dependent kinase inhibitor 2A/B (CDKN2A/B) loss is one of the parameters that support the designation of meningiomas as Central Nervous System (CNS) WHO grade 3 tumors. Evaluation of CDKN2A/B by sequencing or Fluorescence in situ hybridization (FISH) is costly and not always readily accessible. An immunohistochemistry (IHC)-based marker for the evaluation of CDKN2A/B loss would provide faster results at a lower cost.

Methods: This retrospective study included patients diagnosed with meningioma at our institution between 2016 and 2019. Archival tumor tissue was used for analysis. MTAP immunohistochemistry (IHC) was performed at various dilutions (1:1200, 1:400, 1:200, 1:100) using two different antibodies, and p16 IHC was conducted simultaneously. These analyses were carried out at two different institutions. To determine the sensitivity and specificity of MTAP and p16 as surrogate markers for CDKN2A/B loss, CDKN2A FISH was utilized as the gold standard.

Results: Overall, 46/49 tumors showed strong MTAP staining (94%) at institution 1, and 44/49 (90%) showed either faint positive or positive results at institution 2. One grade 3 meningioma that demonstrated homozygous CDKN2A loss by FISH also showed loss of MTAP expression by IHC. One grade 2 meningioma showed regional CDKN2A loss by FISH and variable MTAP expression under different IHC conditions. MTAP expression evaluation was superior at a dilution of 1:100 with the Abnova Anti-MTAP Monoclonal antibody.

Conclusions: P16 expression was variable and did not correlate with either MTAP expression or CDKN2A FISH results. MTAP IHC is a promising surrogate marker for the evaluation of CDKN2A status in meningiomas.

Keywords: CDKN2A; CDKN2B; FISH; IHC; MTAP; meningioma; p16.

Figure 1

MTAP, p16, and FISH results for case #36. (A) H&E-stained section. (B) MTAP expression with 1:200 dilution at institution 1. (C,D) Faint positive p16 expression, institution 1 and institution 2, respectively. (E) Retained CDKN2A with two green and two red signals. (magnification = 600X).

Figure 2

MTAP, p16, and FISH results for a grade 3 meningioma with CDKN2A deletion (case #47). (A) H&E-stained section. (B) Absence of MTAP expression (1:100 dilution). Tumor cells do not stain with MTAP, whereas macrophages show positive staining. (C) Absence of MTAP expression in tumor cells (1:100 dilution). (D) Absence of p16 expression in tumor cells (institution 2). (E) Faint staining with p16 (institution 1). (F) CDKN2A loss with the absence of red signals. (A–E) scale bars = 200 um, (F) magnification = 600X.

Figure 3

MTAP, p16, and FISH results of #30. (A,B) Grade 2 meningioma showing focal MTAP expression at 1:200 and 1:100 dilutions (institution 1), respectively. (C) Positive p16 expression in tumor cells. (D) Absence of p16 expression in tumor cells. (E) Areas with retained CDKN2A with two red and two green signals. (F) Area with CDKN2A loss with the absence of red signals in most nuclei. (A–D) scale bars = 200 um. (E,F): magnification = 600X.

Figure 3

MTAP, p16, and FISH results of #30. (A,B) Grade 2 meningioma showing focal MTAP expression at 1:200 and 1:100 dilutions (institution 1), respectively. (C) Positive p16 expression in tumor cells. (D) Absence of p16 expression in tumor cells. (E) Areas with retained CDKN2A with two red and two green signals. (F) Area with CDKN2A loss with the absence of red signals in most nuclei. (A–D) scale bars = 200 um. (E,F): magnification = 600X.

Figure 4

Analysis of MTAP protein expression for case #21 (grade 1 meningioma) at different dilutions. (A) MTAP expression at 1:100 dilution at institution 1. (B) MTAP expression at 1:200 dilution at institution 1. (C) MTAP expression at 1:1200 dilution at institution 2. Note strong expression in panels (A,B) and very faint staining in panel (C) Scale bars = 200 um.

Figure 5

Analysis of MTAP protein expression for case #12 (grade 1 meningioma) at different dilutions. (A) MTAP expression with 1:100 dilution at institution 1. (B) MTAP expression with 1:200 dilution at institution 1. (C) MTAP expression with 1:1200 dilution at institution 2. Scale bars = 200 um.

Figure 6

Vysis LSI CDKN2A (P16) (9p21)—Spectrum Orange)/D9Z1 (9p11q11)—CEP 9 Spectrum Green probes (Abbott Molecular, Abbott Park, IL, USA). (A) CDKN2A intact tumor with two red and two green signals. (B) Tumor with loss of red signals but presence of two green signals, indicating homozygous loss of CDKN2A. Magnification = 600X.