In 1987, a cooperative study group consisting of five institutions was formed to determine the relative benefits of magnetic resonance imaging (MRI) and endorectal (transrectal) ultrasonography in evaluating patients with clinically localized prostate cancer (stage Ta or Tb). Over a period of 15 months, 230 patients were entered into the study and evaluated with identical imaging techniques. We compared imaging results with information obtained at the time of surgery and on pathological analysis. MRI correctly staged 77 percent of cases of advanced disease and 57 percent of cases of localized disease; the corresponding figures for ultrasonography were 66 and 46 percent (P not significant). These figures did not vary significantly between readers; moreover, simultaneous interpretation of MRI and ultrasound scans did not improve accuracy. In terms of detecting and localizing lesions, MRI identified only 60 percent of all malignant tumors measuring more than 5 mm on pathological analysis and ultrasonography identified only 59 percent. The MRI and ultrasonography equipment that is currently available is not highly accurate in staging early prostate cancer, mainly because neither technique has the ability to identify microscopic spread of disease. Further evaluation with improved equipment may improve the accuracy of these techniques. (N Engl J Med 1990; 323:621–6.) PROSTATE cancer is the most prevalent cancer in men, the most frequently diagnosed cancer, and the second most frequent cause of death due to cancer in American men.1 2 3 The approach to treatment varies and is dependent on the extent of cancer at the time of diagnosis. Although new imaging techniques have been developed over the past 10 to 20 years to increase staging accuracy and thereby lead to better treatment decisions, the increasing need for cost containment has raised questions about the value of these approaches. Computed tomography was initially used to stage prostate cancer,4 5 6 but since it cannot identify.
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