In 15 out of 38 plasmas from GIST patients harboring c-KIT or PDGFRA mutations in tumor tissues, Maier and colleagues identified ctDNA (circulating tumor DNA) bringing tumor-specific mutations, by the allele-specific Taq-Man duplex PCR allele-specific ligation PCR technique. The gene discussed is PDGFRA; the disease is gastrointestinal stromal tumor.