Large B-cell Lymphoma With IRF4 Rearrangement in the Elderly.

Large B‑cell lymphoma with IRF4 rearrangement (LBCL‑IRF4) predominantly affects children and typically presents with Waldeyer's ring and/or head and neck involvement, limited stage, and favorable outcomes. Reports in older adults are rare, and comparability to pediatric disease remains uncertain. We describe an elderly LBCL-IRF4 case with a solitary parotid lesion. Histology showed diffuse large B‑cell lymphoma, germinal center B‑cell type, with co‑expression of CD10, BCL6, and IRF4/MUM1. Karyotyping identified t(4;6)(p14;p25) involving 6p25 (IRF4), and fluorescence in situ hybridization confirmed interferon regulatory factor 4 (IRF4) rearrangement. The patient achieved an excellent response to R-CHOP therapy, resulting in a complete response. Although clinically similar to pediatric cases, this case involved a non‑immunoglobulin translocation partner, contrasting with the pediatric predominance of immunoglobulin loci. Adult LBCL-IRF4 shows heterogeneity, with some cases resembling pediatric presentations and others diverging. This case underscores the need for further research into age-related clinical and molecular differences in elderly LBCL-IRF4.