Reduction of glucose metabolic activity is more accurate than change in size at predicting histopathologic response to neoadjuvant therapy in high-grade soft-tissue sarcomas.

Purpose: Change in tumor size as classified by Response Evaluation Criteria in Solid Tumors poorly correlates with histopathologic response to neoadjuvant therapy in patients with soft-tissue sarcomas. The aim of this study was to prospectively evaluate whether positron emission tomography with (18)F-fluorodeoxyglucose (FDG-PET) allows for a more accurate evaluation of histopathologic response.
Experimental Design: From January 2005 to January 2007, 42 patients with resectable biopsy-proven high-grade soft-tissue sarcoma underwent a FDG-PET/computed tomography scan before and after neoadjuvant treatment. Relative changes in tumor FDG uptake and size from the baseline to the follow-up scan were calculated, and their accuracy for assessment of histopathologic response was compared by receiver operating characteristic curve analysis. Histopathologic response was defined as > or =95% tumor necrosis.
Results: In histopathologic responders (n = 8; 19%), reduction in tumor FDG uptake was significantly greater than in nonresponders (P < 0.001), whereas no significant differences were found for tumor size (P = 0.24). The area under the receiver operating characteristic curve for metabolic changes was 0.93, but only 0.60 for size changes (P = 0.004). Using a 60% decrease in tumor FDG uptake as a threshold resulted in a sensitivity of 100% and a specificity of 71% for assessment of histopathologic response, whereas Response Evaluation Criteria in Solid Tumors showed a sensitivity of 25% and a specificity of 100%.
Conclusion: Quantitative FDG-PET was significantly more accurate than size-based criteria at assessing histopathologic response to neoadjuvant therapy. FDG-PET should be considered as a modality to monitor treatment response in patients with high-grade soft-tissue sarcoma.