Genetic Profiling Reveals the Distinctions Among MTX‐Associated DLBCL, EBV‐Positive Mucocutaneous Ulcer, and EBV + DLBCL

The WHO recently changed the outline of immunodeficiency/dysregulation (IDD)-associated lymphoproliferative disorders (LPDs)/lymphomas from underlying IDD settings to an overarching framework and accommodates commonalities in histology, the involvement of various oncogenic viruses, and specific clinical/therapeutic consequences. A mutational analysis has been performed on post-transplantation and HIV-positive lymphomas, but not on other iatrogenic immunodeficiency (OII)-associated LPDs mainly caused by methotrexate (MTX) to treat rheumatoid arthritis. We herein conducted next-generation sequencing (NGS) to examine the genetic spectrum along with a fluorescence in situ hybridization analysis of 9p24.1 and PD-L1 expression in 37 MTX-associated diffuse large B-cell lymphoma (DLBCL) cases, 17 Epstein-Barr virus (EBV)-positive mucocutaneous ulcer (EBVMCU) cases, and 26 EBV-positive DLBCL (EBV + DLBCL) cases. Targeted NGS identified 177 mutations. The mutation frequency was significantly higher in EBV^- MTX-DLBCL than in EBV-positive LPDs/lymphomas (EBVMCU, EBV⁺ MTX-DLBCL, and EBV + DLBCL). Regrowth or resistance to spontaneous regression after MTX withdrawal was more likely in EBV^- MTX-DLBCL than in EBV⁺ MTX-DLBCL. Therefore, accumulated gene mutations, sustained by the restored immune status in EBV^- MTX-DLBCL, may affect clinical outcomes after MTX discontinuation. Several unique genetic findings were obtained for each category. Fewer TET2/DNMT3A and CD58 mutations in OII-LPD/lymphomas (EBVMCU and MTX-DLBCL) than in EBV + DLBCL indicate that clonal hematopoiesis and an immune evasion-related background contributed less to lymphomagenesis in OII-LPDs. MYD88^L265P/CD79B^Y196 mutations were only detected in EBV^- MTX-DLBCL. SOCS1 mutations were significantly more frequent in EBV-positive LPD/lymphoma categories, irrespective of the immune status, than in EBV^- MTX-DLBCL. These results reveal distinct genetic features among MTX-DLBCL (EBV+/-), EBVMCU, and EBV + DLBCL.