Diffuse Large B‐Cell Lymphoma Presenting in a Background of Rosai–Dorfman Disease

Rosai–Dorfman disease (RDD) can present with lymphadenopathy. However, it is important to note that RDD can also coexist with hematologic malignancies, including non‐Hodgkin lymphomas. We present a case of an older male patient with generalized lymphadenopathy who was first diagnosed with RDD. High‐dose steroid therapy was rendered without a satisfactory response. Thus, the tissue specimens were re‐examined, and the patient was found to have diffuse large B‐cell lymphoma (DLBCL) in the background of RDD. The laboratory tests are notable for a slightly elevated serum lactate dehydrogenase (LDH) level. A positron emission tomography‐computed tomography scan revealed generalized hypermetabolic lymphadenopathy above and below the diaphragm. A bone marrow biopsy showed normocellular marrow without evidence of DLBCL. The international prognostic index score was 3 (age > 60 years, elevated serum LDH level, and Stage III disease), indicating a high‐intermediate risk disease. The patient was treated with six cycles of golcadomide in combination with R‐Pola‐CHP (rituximab, polatuzumab vedotin, cyclophosphamide, doxorubicin, and prednisone) for the underlying DLBCL, with resolution of both DLBCL and RDD. The disease remained in remission at the follow‐up visit 9 months after completing the therapy. This case highlights the importance of recognizing underlying DLBCL in patients with RDD for optimal patient outcomes. Trial Registration: ClinicalTrials.gov identifier: NCT04884035