Abstract
Abstract Background In routine pathology, in situ quantification of protein in formalin-fixed, paraffin-embedded (FFPE) tissue is limited to immunohistochemistry (IHC) which is semi-quantitative at best. Accurate and robust measurement of protein expression in FFPE samples, without loss of morphological information, is currently not achievable. Quantitative protein assessment of FFPE tissue can be destructive, and/or time consuming with risk of analyzing non-relevant tissue due to heterogeneity. We have developed a new reliable quantitative IHC (qIHC) method based on a novel amplification system that enables quantification of protein directly in FFPE tissue by counting dots using a standard bright field microscope. The qIHC method combines the ease, speed and morphological information gained from classical IHC staining together with quantitative assessment of protein expression in situ. The goal of this study was to assess the analytical performance of qIHC in a HER2 assay analyzing both FFPE cell pellets and breast cancer specimens. Methods Five different cell lines with HER2 expression ranging from undetectable with IHC to strongly positive (IHC 3+) were used as test samples. Flow cytometry, and ELISA were used as reference methods to confirm protein expression levels and stability of the cell lines. The qIHC assay was conducted using an automated Autostainer Link 48 stainer, and quantitative assessment was done by counting dots per cell using an image analysis algorithm. Repeatability, reproducibility, robustness, linearity, sensitivity, and quantification limits were evaluated. In addition, 44 breast cancer specimens were stained to compare standard HER2 IHC with qIHC. Results We validated the quantitative test through testing for accuracy, reproducibility, repeatability, robustness, and precision. Each of the different tests showed statistical significant results (p: <0.0001-0.005). The dynamic range and linearity of the assay were investigated by correlating the qIHC results to an in-house-developed flow cytometry assay as well as an FDA-approved ELISA kit for HER2 measurement. All tests demonstrated statistically significant correlation (p: 0.0002-0.0045). No overlap was seen between the different cell lines and a broad dynamic range could be demonstrated ranging from 1*103 receptors/cell up to 2.5*106 receptors/cell. Furthermore, HER2 was clearly detectable above background in the low expression cell line MDA-MB-468, thus showing the inherent high sensitivity of the qIHC assay. To demonstrate the capability of the qIHC assay in tumor tissue, we tested the qIHC concordance to HER2 IHC in 44 breast cancer specimens. We confirmed a strong correlation between IHC and qIHC (p: <0.0001). Conclusions The results show that qIHC provides a highly sensitive, accurate, quantitative, and reliable assay for protein expression in FFPE tissue, which could provide better and more precise diagnosis and thus improved personalized cancer treatment. Citation Format: Kristian Jensen, Rikke M. Jørgensen, Kenneth H. Petersen, Jesper Lohse, Helene Derand. A new quantitative in-situ IHC method - validation of analytical performance. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4568. doi:10.1158/1538-7445.AM2014-4568
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