Complete remission of follicular lymphoma after SARS-CoV-2 infection: from the "flare phenomenon" to the "abscopal effect".

In a 61-year-old patient affected from follicular lymphoma, end-of-treatment [18F]FDG-PET/CT (panel B) revealed bilateral pneumonia suggestive for COVID-19, subsequently confirmed by a nasal swab. Simultaneously, images showed the shrinkage of a para-aortic lymph nodal lesion compared to baseline (arrows), consistent with a partial response to R-bendamustine (panels B–F vs A–E). Re-staging [18F]FDG-PET/CT, obtained after SARS-CoV-2 recovery, showed an increase in size and in [18F]FDG avidity of the para-aortic lesion, suggestive for progressive disease (panels C-G-I). During COVID-19 infection and after, he did not experience any symptoms [1]. Surprisingly, malignancy was excluded by CT-guided biopsy performed twice, and this finding was confirmed by a second follow-up scan showing a complete metabolic response (panels D–H).

Complete remission after a concurrent infection has been reported in diffuse large B-cell lymphoma [2] and Hodgkin lymphoma [3].

The SARS-CoV-2 infection has proved to trigger an immune response. In this patient, the virus may have firstly induced a local “flare phenomenon” (panels C-G-I)—as typically observed in patients receiving immunotherapy—finally resulting in an “abscopal effect” (panels D–H). This report suggests a close interplay among COVID-19 infection, inflammation, and tumour biology.