Comparison of Immunohistochemistry Assay Results with Gene Expression Profiling Methods for Diffuse Large B-Cell Lymphoma Subtype Identification in Matched Patient Samples

Background: The cell of origin (COO) in diffuse large B-cell lymphoma (DLBCL) has prognostic importance. While the COO was originally classified into germinal center B-cell (GCB) or activated B-cell (ABC) subtypes by microarray analysis, routine use was not practical. Immunohistochemistry (IHC)–based methods are widely used with varying results due to lack of standardization. Several classification methods have been developed recently; understanding the concordance between these and existing methods is essential to their practical application. Therefore, we evaluated concordance between 3 commercial assays: a standardized Hans-based IHC method and 2 gene expression profiling (GEP) methods and compared these to the accepted microarray classification.Methods: 137 DLBCL-confirmed tumor samples were evaluated using a standardized Hans-based IHC method for GCB or non-GCB subtype, by a published microarray-based assay, a digital gene expression-based Lymphoma Subtyping Test (LST) and a next-generation sequencing-based assay (EdgeSeq COO). Subtype calls from the 3 GEP methods were harmonized to “GCB” or “non-GCB” and assessed for concordance.Results: Concordance between the Hans-based IHC assay and the microarray-based assay, LST assay and EdgeSeq assay was 79.6% (N=137), 80.0% (N=125) and 78.2% (N=64), respectively; the positive percent agreement (PPA) in non-GCB was 88.9%, 87.0% and 78.1%, respectively. Concordance for the Hans-based IHC assay versus GEP methods was especially high for direct GCB calls (91.0%, 88.3% and 78.1% for microarray, LST and EdgeSeq COO methods, respectively). The newly developed GEP assays performed well against the microarray GEP method, against which they were calibrated (concordance 93.7% and 87.5% and PPA 94.3% and 92.9%, respectively, for LST and EdgeSeq COO).Conclusion: These results demonstrated good consistency between various platforms for stratification of DLBCL into COO subtype classifications. Application of a standardized Hans-based IHC assay offers a robust, rapid and easily accessible platform to classify DLBCL into prognostically important subtypes.