A case of diffuse large B-cell lymphoma achieving complete remission with epcoritamab after pseudoprogression.

Although the use of bispecific antibodies for relapsed/refractory diffuse large B-cell lymphoma (R/R DLBCL) is expanding, reports of pseudoprogression following this therapy are scarce. A 58-year-old, male patient with DLBCL achieved a complete response (CR) after fourth-line therapy with lisocabtagene maraleucel. However, 26 months post-infusion, he experienced the development of pelvic lymphadenopathy, which was histologically confirmed as a relapse. Because the disease was refractory to radiotherapy and chemotherapy, epcoritamab was administered as the seventh-line treatment. A fever developing after the second step-up dose (Cycle 1, day 12) was diagnosed as grade 1 cytokine release syndrome and was treated with acetaminophen. Nonetheless, the fever was still present on day 14, when abdominal pain requiring opioid administration also developed. Computed tomography (CT) revealed enlargement of the pelvic lesions and increased ascites. Cytology of the ascites revealed no lymphoma cells and showed a predominantly inflammatory cell composition, while lactate dehydrogenase levels decreased, supporting the diagnosis of pseudoprogression. The treatment was continued and his symptoms gradually improved. After three cycles, positron emission tomography-CT confirmed the complete metabolic response (CMR), which was maintained through nine cycles. The present case highlights the potential for pseudoprogression to occur during epcoritamab therapy, suggesting that continued treatment may lead to durable remission even in patients with early clinical deterioration.