PURPOSE Given the paucity of data regarding circulating tumor DNA (ctDNA) as a modality to guide diagnosis and treatment for children with advanced solid tumors, we conducted a prospective study to characterize the frequency and clinical impact of diagnostic and targetable genomic variants identified by clinical ctDNA testing. METHODS Our study cohort included 36 children and young adults with advanced solid tumors enrolled in the prospective, multicenter molecular profiling GAIN study. Tumor samples underwent next-generation sequencing, and serial blood samples were analyzed by the FoundationOne Liquid Companion Diagnostic ctDNA test. We evaluated the prevalence of ctDNA in our cohort using ctDNA tumor fraction (TF), the prevalence of genomic variants in ctDNA compared with those in tumor tissue stratified by ctDNA TF, the association between ctDNA TF and radiographic disease response, and the clinical impact of ctDNA testing. RESULTS In our cohort, 67% of patients had at least one liquid biopsy sample with detectable ctDNA by TF. Most patients (72%) had detection of a clinically relevant genomic alteration in at least one ctDNA sample. Most (85%) short variants and translocations identified in tissue were present in ctDNA when TF ≥ 1%, with variation by tumor type. We demonstrated statistically significant differences in absolute ctDNA TF changes among patients with radiographic disease progression (mean, +12.2%, standard deviation, 18.7%) and response (mean, –23.4%, standard deviation, 30.6%), P < .001. ctDNA results affected the clinical care of 26% of patients. CONCLUSION ctDNA is prevalent across a wide range of advanced pediatric solid tumors, identifies clinically important variants, changes with radiographic disease burden, and has a clinical impact.
Roberts et al. (Fri,) studied this question.