Role of ctDNA in surveillance monitoring in nonprogressors. (A) Serum samples collected after therapy in 8 patients who achieved a complete response and underwent surveillance but did not progress clinically. The assigned patient numbers are on the left. Histology: patients 1, 8, and 316, ALK⁻ ALCL; patients 3, 14, and 221, ALK⁺ALCL; patient 12, PTCL-NOS; and patient 15, AITL. (B) The pattern of fluctuation of quantitative ctDNA levels of patients 1 and 15 with multiple time points of detectable ctDNA after therapy but no overt clinical relapse. The x-axis represents time since the on-study date in months and is different for each graph. The y-axis represents the log10 of the quantity of each dominant clonotype (in clonotypes per milliliter). Each colored line represents a different clonotype. The horizontal gray line represents the median level of baseline ctDNA. The dashed vertical line represents EoT, the red vertical line represents time of progression, and the black vertical line represents end of follow-up. The green horizontal bar represents time in clinical remission.