The assignment of diffuse large B-cell lymphoma into cell-of-origin (COO) groups is becoming increasingly important with the emergence of novel therapies that have selective biological activity in germinal center B-cell-like (GCB) or activated B-cell-like (ABC) groups. The LLMPP's Lymph2Cx assay is a parsimonious digital gene-expression (NanoString) based test for COO assignment in formalin-fixed paraffin-embedded tissue (FFPET) routinely produced in standard diagnostic processes. The 20-gene assay was trained using 51 FFPET biopsies; the locked assay was then validated using an independent cohort of 68 FFPET biopsies. Comparisons were made with COO assignment using the original COO model on matched frozen tissue. In the validation cohort the assay was accurate, with only one case with definitive COO being incorrectly assigned, and robust, with >95% concordance of COO assignment between 2 independent laboratories. These qualities, along with the rapid turn-around-time, make Lymph2Cx attractive for implementation in clinical trials and, ultimately, patient management.