Preoperative Evaluation of Renal Cell Carcinoma by Using 18F-FDG PET/CT

The number of patients diagnosed with renal tumor has been increasing with the extensive application of ultrasonography and computed tomography (CT).1 Surgical resection remains necessary for a definitive diagnosis of renal tumor, but it is not always clinically beneficial, especially for elderly patients or those with severe comorbidities. For these patients, avoiding surgery and proceeding to active surveillance has become the mainstay of patient management.2,3 Without surgical intervention, the evaluation of tumor malignancy is helpful for treatment strategy decisions such as the timing of surgery or maintaining active surveillance. F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) is a widely used effective modality for evaluating tumor activity by estimating glucose metabolism. The usefulness of FDG-PET imaging in oncology is based on a correlation between glucose metabolism and the degree of tumor malignancy, which has been reported for various tumors.4–12 Although we have observed differential FDG uptake in renal tumor, there are few studies concerning FDG-PET for renal cell carcinoma (RCC), most likely because of difficulties in differentiating the radioactivity of FDG accumulated in renal tumors from the radioactivity of FDG excreted via the urinary system during physiological processes. In addition, false-negative cases can lead to a low sensitivity for RCC detection.13–15 The use of FDG-PET for routine evaluation of renal tumors has not been recommended. However, recently dedicated PET-CT have improved image resolution and signal-to-noise ratio. In addition, attached-CT for photon attenuation correction provides anatomical information on FDG-PET images. A comparison of diagnostic CT and attached-CT facilitates the identification of renal tumors on FDG-PET images, which enable us to place region of interest (ROI) on renal tumor more accurately. Calculation semiquantitative values using these ROI help elucidate the characteristics of FDG uptake of a renal tumor. In this study, we hypothesized that glycolytic metabolism would reflect tumor aggressiveness in renal tumors. Pathological findings such as histological subtype, nuclear grade, and TNM stage are the most widely used indicators for renal tumor aggressiveness.16–18 We investigated the correlation of preoperative renal tumor metabolic activity with tumor pathology. This study applied a semiquantitative value of metabolism as defined by the standardized uptake value (SUV) in a greater number of cases than previously investigated.