About one-third of people who have undergone surgery for colorectal cancer face development of more tumors. However, tests to detect cancer recurrence can give contradictory results, forcing doctors to perform exploratory surgeries that may be too late to be useful. A new study, led by researchers at the Washington University School of Medicine (St. Louis), suggests that positron emission tomography (PET) can detect such tumors early, and reveal the extent to which the cancer has spread. Patients in the study ranged from 26 to 75 years in age and had elevated blood levels of the tumor marker carcinoembryonic antigen, a signal that cancer may be present. Yet imaging methods such as computed tomography failed to reveal new growth. In contrast, PET highlights cells' biological activity, and can visualize a tumor months before it is large enough to be detected by other imaging methods. To undergo these scans, patients are injected with a radioactive form of glucose called fluoro-deoxyglucose (FDG). Cancer cells utilize glucose at a higher rate than normal cells. The FDG-PET images showed that four of the 15 patients with additional cancer had a single tumor. These four underwent further surgery and remained free of cancer for 18 months. E-mail email@example.com.