FDG-PET/CT imaging predicts histopathologic treatment responses after the initial cycle of neoadjuvant chemotherapy in high-grade soft-tissue sarcomas

Abstract

Purpose: In patients with soft-tissue sarcoma (STS), the early assessment of treatment responses is important. Using positron emission tomography/computed tomography (PET/CT) with [(18)F]fluorodeoxyglucose (FDG), we determined whether changes in tumor FDG uptake predict histopathologic treatment responses in high-grade STS after the initial cycle of neoadjuvant chemotherapy.

Experimental design: From February 2006 to March 2008, 50 patients with resectable high-grade STS scheduled for neoadjuvant therapy and subsequent tumor resection were enrolled prospectively. FDG-PET/CT before (baseline), after the first cycle (early follow-up), and after completion of neoadjuvant therapy (late follow-up) was done. Tumor FDG uptake and changes were measured by standardized uptake values. Histopathologic examination of the resected specimen provided an assessment of treatment response. Patients with > or = 95% pathologic necrosis were classified as treatment responders. FDG-PET/CT results were compared with histopathologic findings.

Results: At early follow-up, FDG uptake decreased significantly more in 8 (16%) responders than in the 42 (84%) nonresponders (-55% versus -23%; P = 0.002). All responders and 14 of 42 nonresponders had a > or = 35% reduction in standardized uptake value between baseline and early follow-up. Using a > or = 35% reduction in FDG uptake as early metabolic response threshold resulted in a sensitivity and specificity of FDG-PET for histopathologic response of 100% and 67%, respectively. Applying a higher threshold at late follow-up improved specificity but not sensitivity. CT had no value at response prediction.

Conclusion: A 35% reduction in tumor FDG uptake at early follow-up is a sensitive predictor of histopathologic tumor response. Early treatment decisions such as discontinuation of chemotherapy in nonresponding patients could be based on FDG-PET criteria.

Conflict of interest statement

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Figures

Figure 1

A, ROC curve analysis for predicting histopathologic tumor response by early (dotted line, AUR = 0.60) and late (solid line, AUR = 0.69) changes in tumor size. B, ROC curve analysis for predicting histopathologic tumor response from early (dotted line, AUR= 0.83) and late (solid line, AUR = 0.90) changes in SUVpeak. A decrease in SUVpeak by3 8% was the best early predictor and a decrease by 72% was the best late predictor of histopathologic response. Decreases in SUVpeak by 35% and 60% were the prospectively assigned thresholds.

Figure 2

Changes in SUVpeak after the first cycle (A) and after completion of chemotherapy (C) and early (B) and late (D) changes in tumor size. In 8 of 8 histopathologic responders (), SUVpeak decreased by ≥35% from baseline to early follow-up scan. All but one histopathologic responder (→) showed a decrease in SUVpeak ≥60% from baseline to late follow-up. Neither early nor late size changes were predictive for histopathologic response (B and D). Red, patients who received chemotherapy alone.

Figure 3

Baseline, early, and late follow up FDG-PET/CT in a histopathological responder (A) and a non-responder (B). Changes in tumor SUVpeak and tumor sizes are indicated.