Histological confirmation and radiotherapy facilitate continuation of epcoritamab in a patient with tumor flare reaction.

Epcoritamab, a CD3 × CD20 bispecific antibody, has been approved as salvage therapy for patients with relapsed/refractory large B-cell lymphoma. However, immunotherapeutic agents have been linked to tumor flare reaction (TFR), which is characterized by rapid tumor proliferation associated with the immune response. This report describes the case of a 71-year-old man with relapsed/refractory diffuse large B-cell lymphoma who developed TFR in the cervical lymph nodes during treatment with epcoritamab. Prompt biopsy upon detection of tumor enlargement led to an accurate diagnosis of TFR and informed therapeutic strategies. Subsequent radiotherapy (RT) effectively controlled local lesions while preserving the systemic immune response, suggesting that RT may be an option to prevent the recurrence and progression of TFR and help to avoid discontinuation of effective therapy.