Patients with follicular lymphoma should be treated according to baseline PET-CT findings with targeted re-biopsy.

Although the increasing use of PET-CT has enabled improvements in staging and confirmation of a suspected histological transformation of follicular lymphoma (FL), the disease is still characterised by varied courses and outcomes. Our aim was to determine, whether diagnostic PET-CT could be effective in preventing early progression, particularly disease progression within 24 months of started therapy (POD24). Patient data of 177 grade 1-3a FL patients treated in Oulu University Hospital between years 2000 and 2020 was retrospectively reviewed. Staging of 59 patients included PET-CT before first-line treatment, when excluding two patients who were found to be primary transformed based on their PET-CT. 25 (42.4%) of the 59 patients were also re-biopsied based on the staging results. The control group consisted of 118 non-PET-CT staged patients who received systemic therapy for their disease. The use of PET-CT at the time of the diagnosis was determined by clinician based on the clinical course of the individual patient. In the PET-CT staged group four transformations were noted during follow-up and six cases of POD24 occurred. In comparison, fifteen transformations (p = 0.306) and 18 POD24 (p = 0.486) occurred in the reference group. A high SUVmax was indicative of worse outcomes (p = 0.016) but survival was not improved in the re-biopsied subgroup. Diagnostic PET-CT enhanced disease course as time to progression was superior in the group of PET-CT staged patients (p = 0.038). Our results suggest that PET-CT is a valuable diagnostic tool at baseline which may help to identify patients at risk for POD24 leading to better survival.