[PET-CT positive lesions suggestive of pseudoprogression during long-term follow-up after complete remission with...

A 57-year-old woman with relapsed/refractory diffuse large B-cell lymphoma was under observation after achieving complete remission on chimeric antigen receptor T-cell (CAR-T) therapy with tisagenlecleucel (tisa-cel). There was no evidence of cytokine release syndrome or immune effector cell-related neurotoxicity. Eleven months after tisa-cel treatment, the patient experienced pain on the right side of her body, and was put under active surveillance. ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography showed multiple mass lesions with high uptake, suggesting a recurrence. These lesions spontaneously regressed during follow-up, and subjective symptoms disappeared. CAR-T cells were detected in the peripheral blood at consistently low levels throughout the follow-up period. Pseudoprogression in immune cell therapy is an immune reaction often seen immediately after CAR T-cell infusion, but similar reactions may occur even at a later phase and warrant careful monitoring.