FDG-PET/CT imaging predicts histopathologic treatment responses after neoadjuvant therapy in adult primary bone sarcomas

Objectives The aim of this study was to prospectively evaluate whether FDG-PET allows for accurate histopathologic response assessments in primary bone sarcomas.

Methods Twelve consecutive adult patients (7 females, 5 males; 32±15 yrs) with resectable, primary high grade bone sarcomas were prospectively enrolled. FDG-PET/CT imaging was performed before and after neoadjuvant therapy. Changes in tumor FDG uptake and tumor size were quantified by SUVmax and CT, respectively. Imaging findings were correlated with histopathology whereby a complete response was defined as ≥90% pathologic necrosis in the excised tumor tissue.

Results Stratification of changes in SUVmax by histopathologic response showed that decreases in tumor FDG uptake from baseline to late follow up were significantly more pronounced in histopathologic responders (n=4) than in non-responders (n=8)(64±20% vs. 28±29%; p=0.02). Using a ≥60% reduction in SUVmax as the threshold value for a metabolic response correctly classified 3 of 4 histopathologic responders and all 8 histo-pathologic non-responders (Sensitivity, 75%; Specificity, 100%). Defining metabolic response as a decrease in SUVmax of ≥ 60% and / or SUVmax after neoadjuvant therapy of < 2.5 identified all histopathologic responder and non-responder as true positive. No patient achieved a significant size or volume change in response to treatment.

Conclusions These data demonstrate that changes in SUVmax and absolute post-treatment tumor SUVmax permit the non-invasive identification of patients responding or not responding to neoadjuvant bone sarcoma treatment.