Cancer biopsies are invasive and often painful procedures in which tissue is removed to diagnose and characterize cancer. And after all the trouble involved in taking biopsies, some still don’t provide physicians with enough tumor cells for further molecular analysis. But a day might be coming when biopsies won’t automatically mean removal of tissue. Instead, they will be performed with samples of easily obtained body fluids such as blood or urine. Advances in DNA testing technology are hastening the arrival of such liquid biopsies. Current research on liquid biopsies for oncology is focused on using techniques such as polymerase chain reaction (PCR) measurements of cell-free DNA to guide and monitor treatment. At this point, scientists doubt the technology will be suitable for initial cancer screening, but they hope it will be able to confirm a diagnosis or help when tumor tissue isn’t available. When cells die, they release DNA into ...