"Quadruple-hit" primary testicular diffuse large B-cell lymphoma with MYD88 L265P mutation, IGH::MYC, and IRF4- and BCL6-rearrangements.

Classification of DLBCL relies on clinical, immunohistochemical, and genetic information. We report a case of primary testicular diffuse large B-cell lymphoma (PT-DLBCL) with a hitherto unreported constellation of pathologic findings to illustrate the challenges of DLBCL classification. A standard hematopathology workup was followed by gene expression profiling (GEP) to determine the DLBCL cell of origin (COO). A 75-year-old man presented with a unilateral testicular mass that had developed over the course of 1 month. Pathologic examination demonstrated involvement by DLBCL. Clinical staging revealed no systemic disease. Genetic testing showed an MYD88 mutation, as well as IGH::MYC and IRF4- and BCL6-rearrangements. Gene expression profiling demonstrated an activated B-cell expression profile. This case highlights the genetic complexity of DLBCL arising in the testis and questions the clinical significance of the identified genetic abnormalities.