Interim PET Management and ctDNA-Guided Decisions in DLBCL

Dr. Graff discusses the challenging scenario of a positive interim PET scan mid-treatment. Current practice continues planned therapy without escalation outside clinical trials, and she proactively counsels patients about this possibility at treatment initiation to prevent alarm when scans are incompletely clear.

False-positive considerations are particularly relevant with novel immunomodulatory agents; tumor flare, inflammatory responses, and necrotic changes may produce PET signal without representing active disease. She notes that the subsequent end-of-treatment assessment provides another evaluation point. She advocates for ctDNA as an emerging tool to help interpret equivocal PET findings, sharing personal experience using ctDNA in the relapsed setting to avoid repeat biopsies at difficult anatomic locations.

Dr. Westin discusses the transformative potential of ctDNA for treatment duration decisions, noting that a Columbia University study is prospectively evaluating whether patients clearing ctDNA by cycle 3 might safely stop after 4 cycles. He contextualizes this as the next evolution in a historical trajectory from 8 to 6 cycles of CHOP-based therapy, noting the original 6-cycle convention emerged more from tradition ("2 cycles plus complete response plus 2") than from rigorous evidence. Careful patient selection, particularly selection of those with the lowest relapse risk, is essential before shortening treatment outside a clinical trial.