Clinical uses of ctDNA in lymphoma. (A) An idealized schematic of the course of a patient through initial diagnosis, treatment, and relapse with lymphoma. ctDNA assessment has potential applications throughout the disease course, including mutational genotyping prior to treatment, molecular response assessment at early time points during treatment, detection of residual disease at the end of therapy, and early detection of relapsed disease prior to eventual clinical relapse. (B) The dynamics of ctDNA levels in 14 patients with dense serial sampling are shown as a spider plot. Levels of ctDNA are normalized to pretreatment levels, whereas each line is colored according to the patient’s eventual best response by PET/CT scan. (C) Kaplan-Meier estimates of EFS for patients achieving or not achieving a 2-log decrease in ctDNA after 1 cycle of therapy (ie, EMR). (D) Kaplan-Meier estimates of EFS for patients achieving or not achieving a 2.5-log decrease in ctDNA after 2 cycles of therapy (ie, MMR). Data in (B-D) are reproduced from Kurtz et al¹⁸  with permission. HR, hazard ratio.