Effect of insulin on uptake of FDG by experimental mammary carcinoma in diabetic rats

PURPOSE: To determine whether insulin improves tumor uptake of 2- [fluorine-18] fluoro-2-deoxy-D-glucose (FDG) in diabetic rats with mammary carcinoma. MATERIALS AND METHODS: Rats were inoculated subcutaneously with mammary carcinoma cells. Four weeks later, diabetes was established with streptozocin while controls were given saline. Two weeks later, after overnight fasting, 12 diabetic and 11 control rats received saline and five diabetic rats received insulin 60 minutes before FDG injection (100 μCi [3.7 MBq]). Three diabetic rats received insulin 30 minutes before FDG injection. One hour after FDG injection (ie, at sacrifice), F-18 activity in tumor and normal tissues was measured. RESULTS: Insulin significantly reduced blood glucose levels in diabetic rats at sacrifice. Tumor FDG uptake, which significantly declined with untreated diabetes (P < .005 vs controls), was not significantly different between insulin-treated and untreated diabetic rats. Insulin significantly improved tumor/lung and tumor/live uptake ratios in diabetes (P < .005), although the tumor/muscle uptake ratio significantly decreased to 40% of the diabetic value with insulin (P < .005). CONCLUSION: Diabetes markedly impairs tumor targeting with FDG. In diabetic patients, the judicious use of insulin may improve tumor/nontumor uptake ratios in specific organs such as the liver or lung, although insulin consistently reduces tumor/muscle uptake ratios.