IHC cell-of-origin classifiers for Diffuse Large B-cell Lymphoma 1 Title: Poor concordance among nine immunohistochemistry classifiers of cell-of- origin for Diffuse Large B-cell Lymphoma: implications for therapeutic strategies

Running title: IHC cell-of-origin classifiers for DLBCL Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. IHC cell-of-origin classifiers for Diffuse Large B-cell Lymphoma 2 The authors have no conflict of interest to disclose Text word count: 4374 Number of figures: 3 (1 in supplementary data) Number of tables: 6 (2 in supplementary data) Research. Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. IHC cell-of-origin classifiers for Diffuse Large B-cell Lymphoma 3 Statement of translational relevance: Molecular characterization is opening opportunities for personalized therapy in poor risk Diffuse Large B-cell Lymphoma (DLBCL). Clinical trials using gene expression profiling (GEP) as stratifiers are under way. Immunohistochemistry (IHC) is attractive as a surrogate for molecular stratification in DLBCL and the Hans algorithm is being used to define DLBCL of the Activated B-Cell (ABC) type in clinical trials offering NF-kB targeting agents. However the applicability of IHC classifiers has been questioned. We investigated nine IHC algorithms in a large dataset of diagnostic DLBCLs and report a high degree of disagreement in classifying a single patient by all methods. Moreover none of the methods was able to identify different prognostic groups within R-CHOP treated subjects. We suggest that the application of IHC as an alternative to molecular based approaches should be used with caution. Collaborative IHC studies to provide procedural guidelines for use in the clinical arena are warranted. Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Abstract Purpose: The opportunity to improve therapeutic choices on the basis of molecular features of the tumour cells is on the horizon in Diffuse Large B-cell Lymphoma (DLBCL). Agents such as bortezomib exhibit selective activity against the poor outcome activated B-cell type DLBCL. In order for targeted therapies to succeed in this disease, robust strategies that segregate patients into molecular groups with high reliability are needed. While molecular studies are considered gold standard, several immunohistochemistry (IHC) algorithms have been published that claim to be able to stratify patients according to their cell-of-origin and to be relevant for patient outcome. However results are poorly reproducible by independent groups. Experimental design: We investigated nine IHC algorithms for molecular classification in a dataset of DLBCL diagnostic biopsies, incorporating immunostaining for CD10, BCL6, BCL2, MUM1, FOXP1, GCET1 and LMO2. IHC profiles were assessed and agreed among three expert …