Given the positive relation of ctDNA and tumor volume and to better understand the clinical utility of ctDNA, the present study evaluated ctDNA during the long treatment course of patients with GIST by using the KIT exon 11 ddPCR drop‐off assay [29] and compared changes in ctDNA levels with RECIST and total tumor volume measurements obtained from CT scans. This evidence concerns the gene KIT and gastrointestinal stromal tumor.