Reinke S, et al. - Experts intended to explore the round-robin test to evaluate the interlaboratory variability for the cell-of-origin classification of diffuse large B-cell lymphoma (DLBCL) tumors using the immunohistochemical (IHC) classifier comprising the expression of CD10, BCL6, and MUM1 (so-called Hans classifier). The results in 3/10 cases (30%) revealed discrepancies between centers and/or between IHC and gene expression analysis (GEP) subtype. The first round-robin test was elucidated for COO subtyping in DLBCL using IHC. Yielded results exhibited that COO classification using the Hans classifier displayed consistent results among experienced hematopathologists, even when variable staining protocols were used.