In a key advancement opening future development of personalized tumor biomarker assays, Victor E. Velculescu, from Johns Hopkins University (Maryland, USA), and colleagues have developed a diagnostic test to measure circulating levels of tumor DNA.  Writing that: “Polymerase chain reaction with primers spanning the breakpoints was able to detect mutant DNA molecules present at levels lower than 0.001% and readily identified mutated circulating DNA in patient plasma samples,” the researchers propose that: “This approach provides an exquisitely sensitive and broadly applicable approach for the development of personalized biomarkers to enhance the clinical management of cancer patients.”