Case Report: Fibrosis appearing as disease progression on PET/CT following R-CHOP in newly diagnosed DLBCL

Diffuse large B-cell lymphoma (DLBCL) is a frequently encountered aggressive lymphoma in clinical practice. The immunochemotherapy regimen consisting of rituximab/cyclophosphamide/doxorubicin/vincristine/prednisone (R-CHOP) is a standard first-line therapy that results in complete remission in the majority of patients. Here, we summarize the case of a patient with newly diagnosed DLBCL who, after completing a full 6-cycle course of R-CHOP, exhibited increasing uptake in her original retroperitoneal mass on her end-of-therapy and 3-month post-therapy 18F-fluorodeoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT) scans. Evaluation with further imaging studies, tissue biopsies, and minimally invasive measurable residual disease tests ruled out primary refractory lymphoma. The FDG-avidity of the lesion was attributed to the presence of fibrosis, as it resolved on subsequent PET/CT scans without further therapeutic interventions. This case demonstrates how fibrosis may mimic disease progression on PET/CT after a cytotoxic regimen in DLBCL and should be considered in the differential diagnosis for patients with positive PET/CT scans to potentially spare them from receiving next-line therapy.