Clinicopathological spectrum of CD10 , BCL6 , MUM1 triple‐positive diffuse large B‐cell lymphoma and large B‐cell lymphoma with IRF4 rearrangement

AIMS: Triple-positive diffuse large B-cell lymphoma (TP-DLBCL), co-expressing CD10, BCL6 and MUM1, represents a rare subset with potential associations with IRF4 rearrangements. This study investigated the clinicopathological spectrum and frequency of IRF4 rearrangements in TP-DLBCL and characterised large B-cell lymphoma with IRF4 rearrangement (LBCL-IRF4-R) in a Korean population. METHODS AND RESULTS: We retrospectively analysed 977 DLBCL cases diagnosed between 2003 and 2022. TP-DLBCL accounted for 4.9% (48/977) of all cases. Among 40 eligible TP-DLBCL cases, 17.5% (7/40) harboured IRF4 rearrangements by fluorescence in situ hybridization. Including two double-positive cases, nine LBCL-IRF4-R cases were characterized. TP-DLBCL showed a significant predilection for low-stage disease (stage I-II: 30/40, 75.0%) compared to non-TP-DLBCL (67/143, 46.9%; P = 0.002). LBCL-IRF4-R patients were significantly younger than TP-DLBCL without IRF4 rearrangement (mean age 40.6 versus 59.8 years, P = 0.049) with distinct features including preferential involvement of lymph nodes, tonsils and spleen (6/9, 66.7%), less frequent multiple extranodal involvement (P = 0.041) and conglomerated mass presentation. Most LBCL-IRF4-R cases achieved complete remission, though one adult case with MYD88 mutation showed aggressive behaviour. Genetic profiling revealed heterogeneous patterns with IRF4 mutations in all sequenced cases, and recurrent PIM1, HIST1H1E and CARD11 mutations. CONCLUSIONS: LBCL-IRF4-R represents a clinically and molecularly heterogeneous entity extending beyond paediatric populations and head-and-neck locations. IRF4 fluorescence in situ hybridization testing should be considered in TP-DLBCL cases, particularly in younger patients with localized disease.