Late FDG PET normalization after radioimmunotherapy in a patient with non-Hodgkin lymphoma

Fluoro-deoxy-glucose positron emission tomography (FDG PET) has largely been used for response assessment after treatment of lymphoma, resulting in a very sensitive and specific imaging technique for the detection of residual disease. For this reason FDG PET has recently been proposed to be integrated in the International Workshop Criteria. In this report, a patient with non-Hodgkin lymphoma was treated with radioimmunotherapy for disease relapse, demonstrated by PET. Post-treatment evaluation was performed 9 weeks after treatment, and PET showed almost complete disappearance of tracer uptake, but with faint persistence of uptake at 1 iliac node and thus was a suspect for residual disease. However, a wait-and-see approach was decided and the patient was rescanned with PET 18 weeks after treatment, and the results were finally negative. This case indicates that after completion of radioimmunotherapy it may be recommended to wait several weeks before performing a PET scan and, in case of minimal findings, to consider a short-term re-evaluation.