P5-11-04: A New Immunohistochemistry-Based Assay SBrC5 Classifies Invasive Breast Cancer Subtypes – Profiling Five Biomarkers in One Single Test.

Abstract

Abstract Background: Obtaining expression status of estrogen receptor (ER), progesterone receptor (PR) and Her2 is essential for guiding treatment and predicting outcome for breast cancers. By adding cytokeratin 5/6 and EGFR to the above mentioned three common biomarkers, a five-biomarker breast cancer panel has been validated in previous studies for identifying the basal-like subtype with superior prognostic values than the triple negative subtype1. The current study aimed to evaluate a new immunohistochemical assay, named Subtyping Breast Cancers 5-in-1 Assay (abbreviated as SBrC5, or “the assay” in this poster), for classifying breast cancer subtypes. Material and Methods: A cocktail of ER, PR, Her2, cytokeratin 5/6 and EGFR antibodies (SBrC5 Cocktail) and the MultiVision Detection Kit (TFS Cat. #: TL-012-MARH) were used in generating the data for this poster. The Multivision Detection Kit is a double staining system with two visualizing colors, red and blue. The assay was performed on a breast cancer tissue microarray containing 75 cases in duplicate. Both color and cellular localization of the staining generated from the assay was used for the result interpretation. There were three staining clusters: 1) Red Nuclei indicated ER or PR positive; 2) Red Membrane indicated Her2 expression; and 3) Blue Membrane or Cytoplasm indicated EGFR or cytokeratine 5/6 positivity respectively. The same breast cancer tissue microarray was also subjected to individual IHC tests of ER, PR, Her2, cytokeratin 5/6 and EGFR. The concordance between the assay and the individual tests was analyzed. Results: The assay SBrC5 was found to have excellent effectiveness in detecting ER or PR positivity, Her2 over expression, and cytokeratine 5/6 or EGFR positivity. The concordance for the assay when compared to the individual tests for each biomarker were 94.1%, 93.8% and 92.4% for Her2, combined results of ER and PR, and combined results of cytokeratine 5/6 and EGFR respectively. When a similar comparison was made, the sensitivity was 87.9%, 94.3% and 73.7%; the specificity was 100%, 93.1% and 100%. Discussion: This study has demonstrated that a single test of the assay SBrC5 was able to accomplish the collective task of the individual IHC tests of the five-biomarker breast cancer panel. The assay is able to provide sufficient information for classifying breast cancer subtypes with only a single IHC test. Thus it makes it possible to obtain subtypes information in biopsy settings where the tumor tissue obtained is often insufficient for multiple tests required to accomplish such task by existing methods. Reference: Maggie C.U. Cheang, David Voduc, Chris Bajdik, et al. Clin Cancer Res March 1, 2008 14; 1368. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-11-04.