Patients undergoing chemotherapy often must wait months before learning whether the treatment is working. A team at Jonsson Comprehensive Cancer Center at the University of California, Los Angeles, recently showed that it could determine the pathologic response after only a single cycle of chemotherapy.In a study reported about a year ago, the researchers demonstrated that changes in glucose metabolism, as measured by positron emission tomography (PET), are more accurate in predicting pathologic response to therapy than changes in tumor size, as shown by computed tomography (CT). The next question, said Dr. Fritz C. Eilber, an assistant professor of surgical oncology and director of the Sarcoma Program at Jonsson, was: How soon can we detect these changes?PET reveals changes in metabolic function – in this case, an increased demand for sugar resulting from the proliferation of cancer cells. Cancer cells consume much higher amounts of sugar than do normal cells. Thus, researchers can track them using the glucose uptake probe FDG (2-fluoro-2-deoxy-D-glucose).Researchers have reported that they could use a combined PET/CT scanner to determine the pathologic response to chemotherapy after a single cycle of the treatment. Shown are PET images of glucose uptake overlaid onto MRI images for responders and nonresponders prior to treatment and after the initial cycle.Using a Siemens Biograph Duo PET/CT scanner, which allowed the researchers to compare simultaneously acquired images of glucose uptake and tumor size, Eilber and colleagues monitored 50 patients undergoing treatment for high-grade soft-tissue sarcomas. “Effective response” to the treatment was defined as a 35 percent decrease in metabolic activity.They determined within a week that 28 of the 50 patients were not responding to chemotherapy. Typically, efficacy of the treatment is assessed by CT scan after about three months or more have passed. Finding out whether the treatment is working would allow oncologists to switch to other, more effective therapies months earlier than they might have otherwise.This buys doctors – and patients – valuable time.“Patients want to know as soon as possible, ‘Am I taking the right drugs?’” Eilber said. “‘If I have only x amount of time to get on the right treatment, why should I waste three or six months on a drug that’s not killing my tumor?’”The researchers are continuing to follow the original cohort and have launched a clinical trial based on the results of the study, which is detailed in the April 15, 2009, issue of Clinical Cancer Research. In addition, they have begun to test new tracers – specifically, looking at cell proliferation with a technique called fluorothymidine positron emission tomography (FLT-PET). They believe that assessments of a patient’s response to therapy will be even more accurate with this approach.They also are evaluating the use of FDG-PET/CT in other cancer types.