According to JAMA Oncology, detecting mutations in the epidermal growth factor receptor (EGFR) by taking free DNA from circulating blood, which is released by macrophages or tumor cells in the body, is similar in accuracy to detecting EGFR mutations by taking tumor tissue. This technique, called “liquid biopsy,” is a great boon to lung cancer patients undergoing chemotherapy. Tumor biopsies are sometimes risky and difficult to type because of the small amount of tissue.