Abstract：
9p21 deletions involving MTAP/CDKN2A genes are detected in diffuse pleural mesotheliomas (DPM) but are absent in benign mesothelial proliferations. Loss of MTAP expression by immunohistochemistry (IHC) is well accepted as a surrogate for 9p21 deletion to support a diagnosis of DPM. Accurate interpretation can be critical in the diagnosis of DPM, but variations in antibody performance may impact interpretation. The objectives of this study were to compare the performance of MTAP monoclonal antibodies (mAbs) EPR6893 and 1813 and to compare MTAP expression by IHC with 9p21 copy number status in DPM. Cytoplasmic expression of MTAP IHC with mAbs EPR6893 (ab126770; Abcam) and 1813 (NBP2-75730, Novus Biologicals) was evaluated in 56 DPM (47 epithelioid, 7 biphasic, and 2 sarcomatoid) profiled by targeted next-generation sequencing. 9p21 Copy number status was assessed by Fraction and Allele-Specific Copy Number Estimates from Tumor Sequencing (FACETS) analysis and also by CDKN2A fluorescence in situ hybridization in discrepant cases when material was available. MTAP mAb 1813 showed stronger immunoreactivity, more specific staining, and no equivocal interpretations compared to mAb EPR6893 which showed equivocal staining in 19 (34%) of cases due to weak or heterogenous immunoreactivity, lack of definitive internal positive control, and/or nonspecific background staining. MTAP expression with mAb 1813 showed near perfect agreement with 9p21 copy number by combined FACETS/fluorescence in situ hybridization calls (κ = 0.85; 95% CI, 0.71-0.99; P < .001). MTAP IHC with mAb 1813 was 96% sensitive, 86% specific, and 93% accurate for 9p21 homozygous deletion. The findings of this study suggest that interpretation of MTAP IHC is improved with mAb 1813 because mAb EPR6893 was often limited by equivocal interpretations. We show that MTAP IHC and molecular assays are complementary in detecting 9p21 homozygous deletion. MTAP IHC may be particularly useful for low tumor purity samples and in low-resource settings.
摘要：
在弥漫性胸膜间皮瘤（DPM）中检测到涉及MTAP/CDKN2A基因的9p21缺失，但在良性间皮增生中却没有。通过免疫组织化学(IHC)的MTAP表达的缺失被公认为9p21缺失的替代以支持DPM的诊断。准确的解释在DPM的诊断中至关重要，但是抗体性能的变化可能会影响解释。这项研究的目的是比较MTAP单克隆抗体（mAb）EPR6893和1813的性能，并比较IHC的MTAP表达与DPM中的9p21拷贝数状态。用mAbsEPR6893（ab126770；Abcam，剑桥,MA,美国)和1813(NBP2-75730，Novus生物制品，百周年纪念,CO,美国）在56DPM（47个上皮样，7双相，和2个肉瘤样）通过靶向NGS进行分析。9p21拷贝数状态通过FACETS分析以及在材料可用时在不同情况下通过CDKN2AFISH评估。MTAPmAb1813显示更强的免疫反应性，与mAbEPR6893相比，由于免疫反应性弱或异质性，在19例（34％）中显示出不明确的染色，缺乏明确的内部积极控制，和/或非特异性背景染色。通过结合FACETS/FISH调用,mAb1813的MTAP表达显示与9p21拷贝数接近完美一致(Kappa=0.85;95%IC:0.71-0.99,P<0.001)。MTAP与mAb1813的IHC敏感性为96%，对于9p21纯合缺失，其特异性为86%，准确性为93%。这项研究的结果表明，mAb1813改善了MTAPIHC的解释，因为mAbEPR6893通常受到模棱两可的解释的限制。我们显示MTAPIHC和分子测定在检测9p21纯合缺失方面是互补的。MTAPIHC可能对低肿瘤纯度样品和低资源环境特别有用。
