(A) Schematic of clonal evolution in cHL after chemotoxic therapy as determined by ctDNA analysis, with resurgence of the founder clone. (B) Schematic of clonal evolution in cHL after immunotherapy as determined by ctDNA analysis, with emergence of new clone(s). (C) Reduction in ctDNA burden correlates with likelihood of complete response. (Reprinted from Spina V, Bruscaggin A, Cuccaro A, et al. Circulating tumor DNA reveals genetics, clonal evolution, and residual disease in classical Hodgkin lymphoma. Blood. 2018;131:2413-2425.) (D) Probability of progression free survival (PFS) based upon a threshold of 2 log reduction in ctDNA burden. (Reprinted from Spina V, Bruscaggin A, Cuccaro A, et al. Circulating tumor DNA reveals genetics, clonal evolution, and residual disease in classical Hodgkin lymphoma. Blood. 2018;131:2413-2425.)