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

TLDR

Change in tumor size as classified by RECIST poorly correlates with histopathologic response to neoadjuvant therapy in soft‑tissue sarcoma patients. The study prospectively evaluated whether FDG‑PET can more accurately assess histopathologic response to neoadjuvant therapy in high‑grade soft‑tissue sarcoma patients. The authors measured relative changes in FDG uptake and tumor size before and after neoadjuvant therapy in 42 patients and compared their diagnostic accuracy using receiver operating characteristic curves. FDG‑PET changes were markedly more predictive of histopathologic response than size changes, with an AUC of 0.93 versus 0.60, a 60 % uptake decline yielding 100 % sensitivity and 71 % specificity, and outperforming RECIST criteria.

Abstract

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.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.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%.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.