Abstract 544: Lung cancer classification using new immunohistochemical assay with anti-p40 (BC28) mouse monoclonal antibody: Comparison with the p40 Echelon assay and anti-p63 (4A4) antibody
Authors: Dvorak Katerina , Roessler Christian , Palting John , Moh Akira 
Published: August 2015

Background: The precise differentiation of lung adenocarcinoma (ADC) and lung squamous cell carcinoma (SCC) is essential for the determination of appropriate cancer therapy. Currently, the anti-p63 (4A4) antibody is the most frequently used marker for the lung SCC classification. A major limitation of this antibody is low specificity due to its reactivity in a substantial proportion of lung ADCs. The p63 antibody recognizes two p63 isoforms - 1) long TAp63 isoform and 2) a truncated variant designated as p40. In contrast to the anti-p63 antibody, the anti-p40 (BC28) antibody recognizes only the p40 isoform. The goal of this study was to compare a newly optimized IHC assay using the anti-p40 (BC28) antibody and OptiView IHC DAB Detection Kit with 1) the commercially available p40 Echelon assay, and with 2) an IHC assay using the anti-p63 (4A4) antibody in various lung tumors.

Methods: Lung tumors from 271 patients were evaluated for p40 and p63 expression using IHC on VENTANA BenchMark XT platform with OptiView detection. The p40 expression was also evaluated by the commercially available anti-p40 (BC28) Echelon assay (Biocare Medical Inc.) using the manufacturer's recommended protocol. After the initial classification of these tumors by H&E, anti-Napsin A (MRQ-60), anti-Cytokeratin 5/6 (D5/16B4) or anti-TTF-1 (SP141) antibodies were used for the evaluation of the discordant cases when H&E and p40/p63 status did not correlate.

Results: The anti-p40 and anti-p63 antibodies showed nuclear staining with no or minimal background. After resolving discordant cases, the new optimized Ventana assay using anti-p40 (BC28) antibody demonstrated superior sensitivity to the p40 Echelon assay in SCC classification. 92.9% of cases (52/56) showed p40 positive staining with the new p40 assay compared to 73.2% SCC cases (41/56) stained with p40 Echelon assay. In addition, the new p40 IHC assay demonstrated increased specificity compared to the anti-p63 antibody for ADC classification. 7.7% lung ADCs (13/169) were positive with anti-p63 antibody but only 3.0% (5/169) ADCs were positive with anti-p40 antibody. The new p40 assay correctly classified 96.0% SCC and ADC cases while 91.2% and 93.8% SCC and ADC case were correctly classified with p40 Echelon assay and anti-p63 antibody, respectively. All of the other lung tumors were negative for p40 and p63 except one bronchioloalveolar carcinoma case (1/14) and 6 adenosquamous carcinoma cases (6/13).

Conclusion: In summary, the optimized p40 assay shows an improved sensitivity over the p40 Echelon assay, while both these p40 assays demonstrate a higher specificity compared to IHC assay using anti-p63 (4A4) antibody.

Citation Format: Katerina Dvorak, Christian Roessler, John Palting, Akira Moh. Lung cancer classification using new immunohistochemical assay with anti-p40 (BC28) mouse monoclonal antibody: Comparison with the p40 Echelon assay and anti-p63 (4A4) antibody. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 544. doi:10.1158/1538-7445.AM2015-544