Is it time for PET-guided therapy in follicular lymphoma.

Abstract

18F-fluorodeoxyglucose (FDG) Positron Emission Tomography-Computerised Tomography (PET) is now established as the gold-standard imaging modality for both staging and response assessment of follicular lymphoma (FL). In this Perspective, we propose where PET can, and cannot, guide clinicians in their therapeutic approach. PET at diagnosis/pre-treatment is important for staging, with greater sensitivity compared to standard CT and consequent improved outcomes in truly limited stage FL. Small datasets suggesting a high baseline SUVmax identifies de-novo histologic transformation (HT) are not corroborated by data from GALLIUM, the largest prospective study using modern therapies for FL. Nonetheless, the role of baseline quantitative PET measures requires further clarification. The median survival of patients with newly diagnosed FL is now potentially beyond 20 years. Treatment of symptomatic FL aims to achieve remission and optimise quality of life for as long as possible, with many patients achieving a functional cure at the cost of unwanted treatment effects. Several studies have identified that end-of-induction (EOI) PET after initial chemoimmunotherapy for patients with high tumour burden is strongly predictive of both progression-free and overall survival, and EOI PET is being evaluated as a platform for response-adapted treatment. There remain unmet needs: improving the inferior survival for patients remaining PET-positive; and quantifying the PFS and time to next treatment advantage, and additional toxicity of anti-CD20 maintenance in patients achieving complete metabolic remission. In the absence of an overall survival advantage for frontline maintenance, the question of using PET to guide our therapeutic approach is more important than ever in the context of the COVID-19 pandemic.