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Oncology-Clinical Diagnosis: Solid TumorsSarcoma |
1 UCLA, Los Angeles, California
596
Objectives: The aim of this study was to prospectively evaluate whether a change in FDG-PET or a change in CT size after one cycle of neoadjuvant chemotherapy was more accurate at predicting histopathologic response in patients with high-grade soft tissue sarcoma (STS).
Methods: From 2/06 to 8/07 40 patients with resectable high-grade STS were enrolled. All patients underwent baseline, early (after one cycle) and late (after completion of neoadjuvant therapy) FDG-PET/CT scans. Changes in tumor FDG uptake were quantified by SUVmean. Changes in tumor size were quantified by CT. Response was assessed histopathologically following resection. Patients with 
95% pathologic necrosis were classified as responders.
Results: In histopathologic responders (n=8,20%), reduction of tumor FDG uptake after one cycle of chemotherapy was significantly greater (-52%) than in non-responders (-20%)(p=0.006). The reduction of early tumor CT size in responders (-3%) was not significantly different than that in non-responders (+2%)(p=0.15). All responders and 13 (32%) non-responders had a 30% reduction in SUV between the baseline and early scan while 19 non-responders (48%) had a decrease in SUV of <30%. Using a 30% reduction in FDG uptake as the threshold value for a metabolic response discriminated between responders and non-responders with a sensitivity of 100% and a specificity of 59%(p=0.004). By comparison, no patient achieved even a partial response according to RECIST (area under receiver operating characteristic curve for size changes=0.69).
Conclusions: FDG-PET provides an accurate, non-invasive modality to identify histopathologic response after only one cycle of neoadjuvant therapy in high-grade STS. CT had no predictive value at assessing early response to therapy.
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