A recent study may point the way to a blood test for detecting lung, prostate, and other cancers. Blood levels of a family of molecules called serum-free fatty acids (FFAs) and their breakdown products were one- to six-times higher in patients with lung or prostate cancer than in cancer-free individuals. Once tumors were surgically removed, FFA levels dropped sharply within 24 hours. Measuring FFA levels may therefore also help determine how successful a cancer surgery was and monitor whether cancer is returning. The only blood test currently available for prostate cancer, the prostate-specific antigen (PSA) test, often detects cancer where there is none, leading to unnecessary biopsies and complications. So far there is no blood test for lung cancer.