Persistence of PET scan positivity after chemoimmunotherapy for DLBCL

Approximately 80% of patients with diffuse large B-cell lymphoma achieve a complete response after chemoimmunotherapy as defined by positron emission tomography (PET) scan. However, not all patients who fail to achieve a metabolic complete response are destined to relapse. In a number of these patients, the PET scan is falsely positive (ie, 20%-40% in several large series), particularly when the PET scan has a Deauville score of 4. Reflexively intervening with salvage systemic therapy or radiotherapy in these patients is potentially harmful. It seems that very sensitive measurements of circulating tumor DNA might be able to differentiate between patients who are unlikely to relapse and those with residual lymphoma. It is important to remember that lymphoma is not the only condition that can make a PET scan abnormal and to consider an alternate diagnosis that should be managed differently.